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Blog Archives
1/31/09
It Lives! (Got my X and Y axes running on the mill this morning)
Between the wee hours Friday night and the morning today I've gotten the X and Y axis servos mounted and running. The servos are really not tuned yet, but even in their rough state I was able to move the table at 180 IPM! I am not suggesting that is something that will be accurate or even usable, it was just play, but it was fun! I tried for 200 IPM, but the servos started faulting again and I didn't want to spend too much time tuning for a scenario that isn't real anyway.
Meanwhile, I added a new page that gathers up all the stuff I had to do to adapt the HomeshopCNC servos to the IH Mill CNC Kit.
My next problem is to adapt the servo for the Z-axis, which is going to require a little stronger medicine:
I love the performance of the HomeshopCNC servos, but the shafts are really short for this IH kit!
The Many Uses of an Indexable Spotting Drill
I love this YouTube video I first heard about on the PM boards:
It shows this little indexable spotting drill being used on a mill to spot (a spotting drill is the right tool for spotting, not a center drill which has a delicate point to break off!), chamfer, and engrave. They then turn around and spot, center drill, face, external, and internal turn on a lathe.
What a Jack of all trades!
I first saw an indexable K-Tool spotting drill being used for chamfering on the Tormach web site, and as a result bought one. I haven't used it yet as they don't really get to full versatility without CNC. But I expect to start as soon as my CNC mill conversion is done. More news on that this weekend I'm sure.
There's also another PM thread here about combined spotting/chamfering tools.
1/25/09
Lots of Fabrication, Wiring, Testing, and Diagnosing Went on This Weekend. Result? 3 Servos a-Spinning!
My goal for this weekend was to have the enclosure mounted on the rolling tool cabinet and be able to spin all three servo motors. Easier said than done!
Mounting the enclosure was pretty easy, as was installing the electronics and axis modules. Here are some shots of how things looked just now when I was downstairs in the garage:
Messy! It sure is nice that I can use a laptop with the Smoothstepepr...
Very messy wiring. After I get everything working, I'll be milling new panels (using this CNC mill of course) and I'll take that opportunity to build some real wiring harnesses that clean this up!
The wiring is pretty messy, but I'll be rejiggering it to make some real wiring harnesses and clean it up on a future pass. Right now I just want to make it work. Most of my difficulties have been with the C17 card and getting it to reliably deal with servo faults. I haven't yet decided whether the board is flaky, or whether I'm just using it wrong. I do know I have seen it do some pretty odd things. When I got everything into this cabinet, for example, it completely quit closing the relay during the startup sequence. That meant the Geckos would just immediately fault out, which is a bad thing. If you read my diagnosis page, you'll see I keep having this problem over and over. Each time the fix is a little different. This time I got things going again by connecting the switched side of the Start button to the DC supply relay. That ensures it gets closed during the Start cycle regardless of what the C17 chooses to do. As is usual for me, I didn't think of this solution until after I'd slept overnight from a frustrating earlier session.
Now I've got all 3 servos spinning. X tends to fault out, but that's just because I don't have the servos in a very good state of tune. There's liittle point in it until I can get them mounted on the machine anyway because they'll just need returning. Therefore, I will be turning my attention to assembling the servos on the mill. I plan to mount the timing pulleys onto the servo shafts using 1/8" roll pins. This is how IH does it on their turnkey systems and it'll be a lot more solid than trying to use setscrews on the powerful motors I've got. Towards that end, I was researching the proper hole sizes to drill and came across a page from SDP-SI on it here.
It's been a busy, but fruitfull weekend!
1/12/09
Axis Modules Are Done Pending 2 Cables
All three axis modules are now assembled and tested. As I was finalizing the last of the three modules, I decided I wanted a quick disconnect on the signal wires, so I made up a cable out of a male and female DB9, and that looks like it will work well. I just need to make 2 more of those cables for use with the other 2 axis modules.
Here is what a finished module looks like with the quick disconnect:
To install an axis module in the enclosure requires 2 connections--the quick connect is all the signal level stuff, and then there are the main DC power supply + and - that go to bus bars. It should be pretty quick and easy to install one or switch one with another to clear up some issue. I could've skipped the quick connect, but I got to thinking about poking and prodding inside that enclosure on my hands and knees and wanted to make it easier.
What's next?
1. I need to finish making the other 2 quick connect cables. That'll be easy to do during the week, I hope.
2. I need to clean up the enclosure itself, get it mounted on the side of the rolling chest, and get the electronics mounted inside and tested.
3. Last step is I need to install the servos on the mill and then see the axes move.
We're getting closer!
1/4/09
Planning Two More Axis Modules
I got the last issue figured out with the prototype axis module. I had been manually reseting the startup fault on the Geckodrive. They start in a faulted state until you bring the Err/Res line high. So I was just touching a jumper to the Enc+ terminal to do that. For the finished system, the CNC4PC Master Control Board is supposed to handle that function. Initially, I was having a problem getting it to work properly, but it turned out to be due to the fact I hadn't grounded the Enc- to the same ground the CNC4PC board was expecting to use as its reference. As soon as I did that, I started to get reliable behavior.
Following that troubleshooting effort, I spent some time reviewing where the prototype stood and making a wiring diagram to use as a guide with the other axis modules. I want to clean up the wiring from the current cat's cradle to something a little more manageable. I also wanted to make sure I was grounding all the cable shields to keep noise out of the system. Servo systems are extremely sensitive to noise.
I now have a plan for how to wire the remaining two modules. I will also make some very minor changes in the original module to bring it to the same spec as the two additional modules. I can't do the wiring tonight, so hopefully I'll get a free evening next week and then I can be spinning all three servo motors at once!
After that I still have a fair amount of work to do, but the path to getting the mill up and running will look something like this:
- Finish wiring and testing 3 axis modules.
- Drill mounting holes for the axis modules and front and rear panels in the enclosure. Clean up the enclosure of all remaining chips and other debris.
- Drill the mounting holes to mount the enclosure on the rolling cart.
- Paint the enclosure IH blue.
- Install the electronics in the enclosure, button up, and test again.
- Install 3 servos on the mill. Note that this involves a little machine work on the X and Y timing pulleys for set screws.
- Final cleanup and testing of the CNC electronics and servos. Includes servo tuning and other parameter fine tuning.
- Install head on the mill
- Done!
It's getting close, but there's still a lot of work to be done.
Why CNC for a Home Shop?
There is a good discussion over on HMEM where someone asks why anyone would want CNC for a home shop. Their shop instructor told them that for less than 3 identical parts, manual machining could do it faster and cheaper. Here was my response:
First, I would not want to undertake CNC unless:
- I had a decent knowledge of manual machining. How to measure, what the cutting should sound like, how to judge if I'm going too fast and so on. You lose all "touch" with CNC and have to be able to rely on your experience more IMHO. As a home machinist, you can't just be the "button presser" on your CNC. You are the designer, the one who comes up with the fixtures, and all the rest. Solid manual machining experience is a good background for that.
- I was comfortable with computers being a lot bigger part of my shop experience. This is inescapable when you go to CNC. In particular, you will have to deal with CAD, certainly the machine control (Mach3, for example), and possibly CAM software or g-code programming.
- I was comfortable poking and prodding my way through making the electricals work. There are a lot of electricals with CNC, and if you have a hard time changing a light bulb, you don't want to be dealing with the frustrations of a CNC system. This doesn't mean you need to be able to do component-level diagnosis of circuit boards, but you should be handy with a voltmeter and reading a circuit diagram. Like any machine, the CNC will break sooner or later and you'll have to fix it.
Second, I don't buy the instructor's notion that CNC doesn't "break even" until you need to make several copies of a part. There are a lot of advantages of CNC that are apparent very quickly if you have even a little bit of proficiency:
- It requires less tooling. By the time you pay for a nice DRO and power feeds on all three axes you can just about pay for CNC. Not quite, but close. Add up all the other tooling you may have that is no longer required for CNC and CNC will be cheaper. But, you'd need to pay that bill up front, so it may not matter. Also, to take full advantage, you may need to buy a CAM program so you don't have to g-code it all by hand. That gets REALLY expensive and will eliminate most of the cost savings if not all.
- You can do things that just aren't possible or would be very hard with manual machining. Complex flowing curves and engraving are two examples. We have ball turners for lathes, but profiling such shapes and much more complex ones is trivial with CNC. Also, there are operations that a really talented manual machinist can do that I can't do manually, but can easily do with CNC. There is less of a burden on you, the machinist, to develop that fine art, but you will be called on to develop other fine arts.
- CNC can be faster. The CNC can whip out operations a lot faster than I can, at any rate. A big part of my impetus is this productivity. I simply can't build everything I want to build in my shop fast enough eith the hours available to me. If I invest some of those hours up front in a CNC conversion, I can get more projects done later.
- Surface finish and precision can go way up with CNC. Did you experience an immediate improvement in surface finish when you got a power feed for your mill? I did. Can you hand feed on your lathe and get as good a finish as with the power feed? It's really hard for me, and the results are not always reliable. Now imagine if you could dial in the perfect speeds and feeds for every operation via CNC. In fact, through features like CSS, the machine will even vary the lathe spindle speed as you move towards the axis to ensure that perfect cutting speed.
Let's end my post by considering some photos. Here is a set of CNC'd pulleys hot of the machine:
Note the surface finish. How easily can you get that manually? Sure, some part of it is the radically better rigidity of the machine used, but some part is also the perfect feeds and speeds concept I mentioned.
Now consider a more typical HSM project, an upright marine style multiple expansion steam engine. This one was done in a home shop with CNC by jimmibondi (Frank) that won the HMEM November Engine of the Month:
I will venture to say that it wouldn't take me three copies of it for this masterpiece to get done a lot faster and better with CNC than manual machining. Not that you couldn't do it manually, and not that it didn't require incredible craftsmanship to do with CNC, but it would just take a lot longer manually.
With all that said, manual machining is tremendous fun and CNC is not for everyone. It's a hobby, do what you like!
1/3/09
Major Milestone: Spinning a Servo! (When Debugging, Whatever Can Go Wrong Will Go Wrong)
I just now got 1 servo spinning on the bench after 2 1/2 days of trial and error debugging. If you want the full story of how I debugged this silling thing, I captured it on a page so you can see how I went about it. It's a painful process as not all of the relevant information you will need is captured in one single place. Some of it was out there, but a lot of it I just had to figure out on my own.
Here is a concise list of all the things I had to change from my original attempt to run:
- Set CNC4PC Master Control Board DIP switches for G320. It acts funny on the other board types whether or not Err/Res is connected.
- Discovered I had mislabeled the leads from my front panel for the "Start" and "E-stop", so they were connected backwards.
- Reverse the motor connections because they were backwards compared to what the encoder indicated, causing an immediate servo fault.
- In doing #3, I reversed the wrong leads and had to replace the power supply rectifier. I don't think I blew the Gecko, amazingly!
- Connect a 47K ohm resistor across pins 1 and 3 of the G320 to ensure the bridge initializes properly. This was buried in a hard to find Mariss note on CNCZone.
- Now I was getting the servo to hold position, so I played with the tuning trimpots a bit.
- In Mach3, set Step/Dir to ActiveLo. Set pulse width to 5 (the pulse width may be ignored for Smoothstepper).
- Connect "Common" on G320 to +5V on breakout card instead of Ground. Another one that's easy to miss unless you read a lot of posts on various boards!
- Set up the proper motor tuning parameters on Mach3. IH says 115 IPM speed and 0.15g of acceleration, according to another post I found. I also needed 28,240 steps to move 1".
- Set the Smoothstepper jumpers to actually provide +5V to the breakout board. Otherwise, the terminals marked "+5V" are 0V!
Now I can spin the servo this way and that with Mach3. It can still fault if I rapidly change directions at full jog, but that's just tuning and I need to set it properly on the actual machine instead of with servos flopping around on the floor.
I must admit that per the discussion on the Cookbook Blog on the Eternal Servo vs Stepper Jihad, it was a lot harder to spin a servo than a stepper. In general, I encountered a lot of less than obvious things including the CNC4PC DIP switch settings, need for the 47K ohm resistor (that's going to be built into the next generation Gecko servo drives), and bizarre experiences with "Common", which has to be +5V, and which didn't get +5V until the Smoothstepper jumpers were enabled.
Here are some photos of my CNC electronics testing lab on the dining room table (my wife is glad it seems to be working and I'm cursing a lot less!):
12/31/08
The Eternal Servo vs Stepper Jihad Continues
There are a number of "Jihads" in the machinist's world including the indexable carbide tooling versus hand ground HSS tooling debate, and this debate over the value of servos versus steppers in small CNC machines. I have used both and wrote a response when this subject came up over on the HMEM board recently. I thought I would pass along that response here so the points would be preserved:
Aha, the sacred Servo/Stepper/Open Loop/Closed Loop Jihad has made
it here! I have both. There are good
arguments for both. In the end, I have a hard time not going for the
servos if I can afford it. Just as we can say NASA used stepper-based
systems back in the day so therefore steppers are good, we can also
say there are almost no stepper-based VMC's made today, so therefore
servos are better. In fact, the servos way outperform steppers in most
cases, they just cost more, and you may not need (or be able to take
advantage of) that extra performance. We can argue that we don't
care about that extra performance, and we may not, but let's not kid
ourselves that there isn't even the potential for the performance
or that it won't matter to anyone. I agree with most of what
kf2qd says, but I don't agree on the cost point. A servo-based system
is more expensive, but it isn't $1000 per axis! For example, my IH Mill runs
homeshopcnc servo motors at a cost of $235 (I got the fancier ones,
but they have one with encoder for $199 if you're pinching pennies)
for 850 oz in motors, which are pretty stout. Equivalent stepper motor
might be $130 from the same place, so you save circa $69, the cost of
the encoder. Add a Gecko servo drive 320
at $114, which is the same price as a Gecko 201 stepper drive, so no
incremental cost there. The last servo specific piece
I use is a board from CNC4PC called the "Master Control Board". It manages
the servo fault signals from the Geckodrive and costs $48. You wouldn't
really need one with a stepper system, although it could be used to
manage your E-stop and limit switches. The nice thing it does for servo
users is it manages servo fault signals so that a servo fault looks
like an E-stop. What does that mean? A servo fault happens when
the encoder indicates that the motor hasn't been keeping up with the
commands issued by Mach 3. On a Gecko 320, the fault is triggered if
the encoder falls more than 128 steps behind the commanded position.
For my IH mill, each step is 0.7 of a tenth, so an error of 128 means
that axis is off by about 9 thousandths. Note that this will differ
based on the leadscrew pitch, encoder counts, and belt drive ratios
for your machine, but it gives you an idea. In practice what happens
is, I run the CNC program, and if the servos don't fault, I know I was
within 9 thousands, and probably a lot better, of what the program intended.
Equally as important if not more so, the program may have gotten off
by nearly 9 thousandths at some point, but with a servo system, it can
"catch back up", so the error is localized and doesn't carry through
all subsequent moves. If I was running a stepper system, I might be
off by a lot more, and the errors become cumulative. Once I'm off, the
system never catches back up again. In fact, if I start a whole new
part without rezeroing, the error lives on for the new part too! With the servo fault, I can
see by where the machine stopped what it was doing when the error added
up to too much. It's pretty easy to turn down the feedrate (potentially
just for that part of the program and not the whole program too), restart
the program, and try again. If the same happens for the stepper, I have
to start measuring the part to find where the error begins manually.
I may not even be able to measure the beginnings, because they may have
been machined off. In fact, with the stepper, I have no idea if there
error is due to lost steps or some other source of error in the machine.
This makes tuning up your programs a lot harder with a stepper system
than a servo system. It would be ideal if the
controller could actually log where the errors occurred, how far off
things got, and even let me set in software the servo fault limit (maybe
I want to fault if its off by more than a thou, or perhaps I'd like
to be able to change that tolerance at different places in the program).
It's be even better if the position signal made the control dynamically
slow down or otherwise take steps to "do better". I can't really do
that with the rig I describe. I can do a little better with the Rogers
board, but it isn't clear to me how to make that board work without
even more encoders. It's more of an add on to a stepper system. It's
probably not possible at this stage in Mach 3 development to do what
I describe at all, but what I do get seems pretty good to me. In practice, I suspect steppers
lose steps a lot more often than most stepper users think. Many people
complain that the Gecko 320 is "too sensitive" to servo fault. Given
that the fault doesn't happen until they are off a few thou at least
and maybe more, those same people are obviously used to running stepper
systems that silently get off by that much and keep going. It can get a lot worse too.
Servo faults can be caused because the program runs awry and the cutter
is plowing into vises, clamps, tables, and whatever else gets in the
way. The stepper will keep chugging through it even after the cutter
breaks and there is a smoking ruin. It isn't going to take too much
of that sort of thing before the servo will fault and things stop. So to conclude this rather
long essay, do I insist only on servos? No, not at all. I have two machines
set up for steppers and one for servos. I'm happy with each. I'm just
saying that if I can afford the added expense of servos, I think they're
better in every way. I don't see a down side to them other than the
cost. That cost is quantifiable. On my mill, it has cost me an extra
$210 to buy 3 servos instead of 3 stepper motors, and another $48 for
the Master Control Board. I think the extra $258 was well worth it on
this mill. Your mileage may vary!
In response, John Stevenson makes some excellent points that are a good addition to my post:
First a couple of clarifications. Yes the Bridgeport's did
have massive steppers on them, got loads lying about here and they were
only 850 to 1200 oz in on a type 42 motor. Modern type 34 can piss all
over these so it's not the motors. the Bridgy controller / driver unit
was absolute crap. This is the reason why there are so many good mills
out there, they never wore out because they spent more time broken down,
crash one into something and it burnt the output transistors out - full
stop. They were only full stepping and could hold 0,001" but even in
those days 1 thou to NASA was still the same thou it is today. Bob put some good points
about the difference between steppers and servo's and I have no beef
with his explanations, they are 100%. One point that has been missed
though and lets face it this IS a hobby forum is the skills needed to
built both systems. Steppers are cheap and simple easy to mount usually
on existing hardware as they develop maximum torque at low revs. Servo's
develop max torque at high revs meaning you have to gear an axis down
to get any sort of power out of it. Quoting max feed rates isn't
everything in CNC as any G00 moves are not cutting and only costing
you. The main difference for a
beginner is the complexity of the servo system. There are not many good
servo drivers out there for one and all rely on encoder feedback, to
a beginner this often also translates to noise. Read the CAD_CAM_DRO
list, Gecko list and CNC Zone and most of the beginners problems are
caused by electrical noise. There is also a missing link
at the moment in that the larger servo motors require analogue inputs
but affordable controllers use step and direction, Gecko drives can't
power the big servo's like the BOSS 2's and Mach can't power the larger
Fanuc, Baldor and Siemens servo's drives. Rutex tried and failed, the
Pixie convertor card whist seeming to work was withdrawn so there is
a gap. CNC like any new venture
is a steep learning curve and the sooner it flattens out the sooner
you actually start learning and enjoying. Doing a simple stepper system
to cut your teeth on and then progress if far better than throwing yourself
into the top end, never getting a grasp of it and then feeling let down.
Incidentally my big mill,
a Beaver, the same size as a BOSS 2 and built with the same stepper
motors as the BOSS 1's at 850 ox in direct onto 0.2" pitch ballscrews
has been running all day today drilling circular hole patterns with
a 2.5mm drill. These holes are virtually touching and any errors show
up immediately, add to this the machine has graduated dials on as it
shared some components with it's manual stablemate so when it goes home
it's easily checked. Todays run was 11,208 holes and it's parked back
on 0,0,0 two drill used, tomorrow it will be doing the same but different
job and on 3.12mm holes.
I think my personal conclusion on John's comments, which I stated on the board, is that it may be better for first time CNC'ers to try steppers and avoid the complexities that John is worried about.
In any event, I thought the discussion was excellent and the points were worth repeating here.
12/29/08
Flycutting German Style With a Boring Head
Came across this picture recently on a German site:
I'll bet the tool was ground from an old dull endmill judging from the finish, but I could be wrong about that. I would think a small radius would lead to a nicer finish...
Clamping German Style With a Tooling Plate
From the same German site as the flycutter above comes this method of clamping very irregular parts:
The clamps go down the tooling holes...
German Steam Engine: Wunderbar!
All that fly cutting and other work (check out the article, it's really good!) results in this absolutely gorgeous steam engine model with working water injector pump and flyball governor:
Governor connects via linkage to valve below...
12/27/08
Wiring the Mill Enclosure Continues, and Powder Coat is On Order
I have been busily making cables and wiring up the enclosure. There are a lot of connections here! I have my wiring diagram and I am coloring in each connection as I finish making it. Everything is point to point, so I am making little wiring harnesses and trying to keep it neat.
At the moment I'm just trying to get to the point where I can make one axis module active and spin a single servo motor. If that all works, I will assemble and test the other 2 axis modules. After that it will be time to finish up the enclosure. I got a neat powder coating kit from my brother for Christmas, and I just ordered some Ocean Blue powder coat from Caswell Plating. I think the Ocean Blue will match the IH mill blue pretty good. Powder coat is very durable. Not really necessary for this application, but I thought it would be fun to try it out!
Tormach vs IH Base Castings
Interesting to compare the two. Here is Tormach:
Here is Industrial Hobbies:
Looks to me like the Tormach is a little beefier. I'm glad I did an Epoxy Granite fill on my IH; I'll bet it's beefier still! I'm also glad I've got those big ole hockey puck leveling feet to help me adjust. OTOH, I may just find my base is so stiff that shimming it won't adjust a twist out at all and I'll need to shim the column instead!
Shim or No Shim for Twist on Lathes and Mills
One sure way to ignite a controversy is to bring up the topic of leveling as it relates to out of square lathes and mills. There is a school that says you level the lathe's bed and the rest is a function of the machine itself. There is another school that wants to use level as "close to correct" and then run a test bar with further adjustment of the leveling until the lathe cuts without taper. The first school sees this as adding a twist to the bed and is horrified. The second school sees it as a practical solution to a problem and wonders whether the first school realizes that.
Recently the same sort of argument broke out around milling machines, specifically the Tormach. It's an interesting thread, with both sides weighing in. Philbur addresses the purest camp clearly with this remark:
I think that shimming the bed must be the last resort, not the
first, for correcting a tram error. Tramming the table tells you that
the spindle is not perpendicular to the table surface (assuming the surface
is flat!), it doesn't tell you why. The column may not be square to the
table, or the spindle may not be square to the column, or both. Twisting
the bed will most probably mask one error by introducing a second error.
The correct method is to identify each error individually and correct
it without influencing any other alignments.
OTOH, no less an authority than Tormach's Greg Jackson himself says to shim the base instead of the column:
When working to optimize the left/right tram, shimming the front left or right feet under the base is always the first thing to do. The natural assumption is that the stand should be flat and rigid, then you put the machine on it and everything is perfect. The reality of the world is that everything is flexible, even those things that appear rigid. The stand is less rigid than the base of the mill itself and when the 1100 lb mill is placed on the stand, the stand moves a few thousandths of an inch in reaction to the weight of the mill.
Machine geometry can seem straightforward, but it becomes complex when you start to understand the fine details. If you take a perfect machine an put it on a stand which flexes in a non linear fashion under the weight of the machine, then there will be some left/right tram error due to a small twist force on the base. Countering that twist force by shimming the base/column connection point is possible but shimming between the base/stand is easier and probably a more accurate way to correct.
The iron base of the mill goes through both a heat soak stress relief and a vibration stress relief process so residual stresses are unlikely. The stand is a welded fabrication and will always have some residual internal stresses. If some alignment issues show up over time it could be the result of a crash, motion in the iron, or motion in the steel stand. We believe the stand is the most likely source. In the actual manufacturing process each machine base is checked on a large surface plate before the machine is assembled. Assembly and test is not done on a surface plate, but the rather on a three point stance. Instead of sitting on the four corners of the iron base, the machine rests on the back two corners and a round bar in the center front. Since three points determine a plane, this approach ensures that there are no stresses introduced in the machine base during the final test.
I'm with Jackson on this one from a practical standpoint, although he has sent me correspondence claiming that all problems with out of squareness can be traced to a stand that is not level, something I don't agree with. It may be that the base is fine and the column could be shimmed, but if you can do it from the base, that seems an easier/better approach. If nothing else, try it that way first and take some measurements with your DTI to see how close you're coming.
Also note that for this to work out well, you can't bolt the machine to the stand. What you're doing is using leveling feet on the base to jack one corner or another, so the base has to be able to rise and fall relative to the stand.
Some Random Surface Finish Tips When Milling
- Keep a fine finish pass. Use a different cutter than you roughed with for best finish.
- Keep your finish and rouging cutters separated. If you use the same type of cutter for both, start new cutters as finish cutters and move them to roughing after a little while.
- If the finish is down a hole, relieve the upper cutting surface so it won't be in contact with the hole and just cut at the bottom. This will reduce chatter, and works well when profiling with ball nosed end mills as well.
- Use a larger diameter cutter, if possible, as it will flex less.
- Keep the gibs tighter for less chatter.
- Make sure the z gib is tight by lowering the spindle on a aluminum block on the table to put a bit of upward pressure on the head and tighten the gib on my x4 i was able to turn the screw of the z gib by a turn and a half this will reduce most if not all the chatter you might get from the head assembly.
- I've seen Widgitmaster use a spacer to lock the quill on his Bridgeport. I try to cut with the quill locked on my Industrial Hobbies machine whenever possible.
- Try a 4 flute on aluminum for the finish pass. By the time you're ready to finish, there should be ample room for chips to fly and the extra flutes and light depth of cut will make for a nicer finish (the equivalent of more spindle rpm with a 2 flute).
- Lots of folks swear by 3 flute cutters on aluminum.
- Balance the diameter of a ball end cutter versus the rigidity. Remember, the part of the ball near the axis moves slowly. A smaller ball interpolated exposes more of the surface to a faster moving cutter, leading to a better finish. But, the smaller cutter can flex more. Hence the need to balance these two factors.
A couple notes on improving boring accuracy in a CNC mill:
More Boring Accuracy
- Reduce the flex in deep holes on a 2 flute cutter by grinding down one flute. Now the cutter acts like a boring bar.
- Interpolate the hole with the largest endmill that fits (to reduce flex) and leave a small amount for a finish pass with a reamer.
Stabilizing a Round Column Mill Drill
I have not been a fan of the round column mill drills because every time you raise or lower the head, it can rotate a little on the column. This means you lose your position every time you move the head. When I think about how often I crank the head up and down on my Industrial Hobbies mill, the idea of this seems extremely painful. I'd be tempted to go with one of the little Sieg mills of less capacity rather than deal with it. Nevertheless, these mills are quite popular, they are cheap, and a lot of very fine work has been done with them.
There are some potential solutions to the weakness of head rotation. First, I have seen cases of fixing a laser to the head and using it to align. If you can align the spot on a wall 20 feet away to a precision of 0.100", your head will be accurately positioned to just under a thousandth. Mind you, I'd be tempted to use a wall 10 feet away and a reflector to put the laser spot somewhere close to the mill, but it could be done.
Another approach involves physically changing the mill's structure to hold the alignment. I recently came across a fascinating thread in CNCZone where a fellow has built a wishbone stabilizer for just this purpose. Here are some photos:
The last photo shows an indicator in the chuck being run up and down a straightedge to test how accurately the head is held by the wishbone stabilizer. He says it swings as much as 10 thousandths while cranking but settles back down to 3 or 4 thousandths at the end. That's not bad. I'll bet there is a lot of play in the ball joints and there should be a way to build a little stronger wishbone that would be even more accurate. Nice write up!
12/22/08
Getting Parts Indicated in the Lathe Chuck
I liked this little video (other than leaving the key in the chuck, don't do that!):
There are a couple of great tips here. Aside from aligning the part in the chuck with the ball bearing, the use of circular pieces instead of a dovetail on the QCTP is also quite interesting. It also looks like he keeps that indicator on a permanent holder on the lathe's backsplash where it is handy to get to.
12/21/08
Automatic Tool Change for a Small Sieg Mill Using a Compressed Air Kwik Change
This fellow had a stroke of brilliance. Follow on these pictures screen captured from his video:
Straightforward looking tool changer uses a Bimba cylinder that cost about $4 surplus. The lever gives it mechanical advantage over the die spring...
Size of the top of an R8 taper...
Size of a compressed air Kwik Change. An idea is born!
The top of the R8 taper is sawn off. This style taper is probably only suitable for small mills. That part we're sawing off is probably a good thing on a bigger mill. Nevertheless, by cannibalizing an R8, he guarantees a huge selection of tools to modify...
Now clean up the taper on the lathe...
Tap it for a retention knob...
Knobs are made by turning the head of a bolt into a retention knob. This would be painful without CNC on the lathe I think!
A couple of modified tool holders for comparison. Wonder why he didn't just use the air couplings? Probably that brass is just too weak compared to a bolt...
Drawbar and retention ring.
Here is a shot looking up the spindle. The retention ring is what forces the release when the drawbar presses down on the Kwik Change...
Die spring end of the drawbar...
Progress: Wiring Diagram, Board Mounting, et al
You can be forgiven if you don't think I've been doing anything for 3 weeks. Reallity is I've actually been pretty busy. It takes a ridiculous amount of research to figure out how to wire up one of these CNC projects right, so that's a big part of what I've been doing. Ordering various ancillary parts and mounting my various little sub-circuit boards to a big mounting plate that goes in the enclosure would be the other part. Today I got started wiring up. I want to do just enough wiring to verify I can spin one servo sitting on the bench before I do too much else.
Meanwhile, here are some tidbits:
Smoothstepper wiring (more detail on the electronics page):
Compare this to the diagram directly below. Notice I am reversed. That's intentional, I decided to mount the NEMA enclosure on the side of the rolling cabinet that will be closest to the mill...
12/8/08
Hossmachine Sharpens Endmills With a 4th Axis on a Benchtop Mill
If you've never come across Hoss, you owe it to yourself to check out his web site and postings on CNCZone. He is one of the most inspirational (if not THE most inspirational) CNC "hobbyists" I've come across. Aside from the guys that build cool machines from scratch, there isn't much that Hoss hasn't done. His Sieg X2 has been transformed into a hobbyist vertical machining center. He built a rotary tool changer, flood coolant enclosure, and many other add-ons until it has become an incredible little machine. When I need a fresh shot of inspiration to get off the video games and get back into machine work, I just watch a few of his YouTube videos and I am fired up and ready to go.
The latest thing he has done that caught my eye is this endmill sharpening rig:
Sharpening an endmill on a 4th axis milling machine...
He's got a DeWalt Laminate cutter attached to the regular X2 spindle to provide a high speed spindle option, and he has placed a Dremel grinding point in the collet for this test. The 4th axis guides the cutter along the endmill's helix perfectly. Looks like it got real sharp too!
Home Shop Machinists are always interested in tool and cutter grinding for some reason. I agree T&C cutters are interesting, but it is kind of a big expense to have one sitting around and seldom used. This rig Hoss put together leverages things like the 4th axis and laminate cutter that are useful for a lot of other purposes. Looks to me like the hardest thing about it would be the g-code. We need someone to write a Mach 3 wizard to generate it for any size endmill and then we'd really be in business!
12/2/08
Getting Geared Up to Wire the Box
I've been getting in a plethora of odds and ends to start wiring up the enclosure. I've now got everything except a relay I will use for the E-stop circuit and the master AC on/off switch for the front panel. I also did a number of versions of the overall schematic. The latest is on the enclosure page. Based on my latest schematics, I've done a layout for how I'll go about mounting the various sub-boards in the enclosure:
My goal this weekend would be to get the enclosure to the point I can actually mount the boards and begin the wiring process next weekend, and hopefully try spinning some servos (though not on the machine) next weekend as well. There's quite a bit of work to do there, but if I get enough hours I should reach that stage. Fingers crossed!
I still need to make an arm to support the keyboard and monitor, I need to mount the enclosure to the rolling cabinet, and I also need to paint it.
There's still a lot of fussing. I haven't spec'd or ordered any of the auxilliary panel connectors, for example. I have some sitting around the parts bin that will hopefully work. Have to look at them as well. If need be, I can delay VFD and coolant wiring until after the servos are running and it would be no big deal.