[riabma]

Interesting issue about the pulleys...
Yesterday I have been machining some aluminum parts and I programmed a second finish pass at 3000 rpm with the same feeds. The finish is much better. You can still seeing the 'waves' but after sandblasting with glass bead the finish is great.
Ricardo.

[Steve Seebold]

Interesting issue about the pulleys...
Yesterday I have been machining some aluminum parts and I programmed a second finish pass at 3000 rpm with the same feeds. The finish is much better. You can still seeing the 'waves' but after sandblasting with glass bead the finish is great.
Ricardo.

I do my finish cuts at 4,000 RPM with feed rate 20 so 25 IPM, then I put my parts in a vibratory tumbler with ceramic media for about an hour and they come out almost polished.

Then if I want a better finish, I put them back in the tumbler in crushed walnut shells and jewelers rouge. That polishes them. Only problem with this procedure is, it takes a couple of days.

I did a test batch of parts once. I let them run in the walnut shells for a week, and they came out with a finish I could use as a mirror to shave with.

[riabma]

Hello to everybody,

I have been thinking all this time and I decided that I am going to keep my Tormach. I am still looking for a production machine and I will use the 1100 like a second machine, prototyping, fixtures, etc...

I had my first contact in machining with the Tormach and (it can sounds very silly, hehe...) and I am very attached to the machine. I learned a lot of things and I want to keep it for a LONG time.

I appreciate all your comments and feedback all this time. They were really helpful.

Thanks!

Ricardo

[Steve Seebold]

Good choice Ricardo, but if you want a production machine, if memory serves me correctly, you were talking about a Haas Mini2. They are a nice LITTLE machine, but if you have the room, I could consider a VF1 or a VF2.

If you go with the Mini, you'll be giving up a considerable amount of Z axis capacity.

[mike sr1]

I installed the Fenner belt, that may have helped a bit but not much.

I removed the motor and balanced the pulley as best I could(helped somewhat), the vibration is coming from the motor, and pulley combination or at least most of it.
The motor is a 1715 rpm, and at that rpm up to about 3600 rpm the balance of the rotor is good, past that it isnt so good, but it is being used out of its design balance range with the addition of the VFD.

There is no set screw to hold the pulley on the shaft, a center bolt is used to do that but it allows the key and shaft to float inside the pulley, I used locktite on mine so it wouldnt move and produce wear between the two components.

From what i see so far to get a better balance the armature, pulley assembly needs to be rebalanced up to the maximum VFD rpm. That may well prove to be expensive.
The spindle pulley I havent checked yet as most of the vibration seems to come from the motor and pulley assembly.

My machine seems to be good up to just under 4000 rpm so thats what I will use for the time being......

[TurboStep]

I originally wanted to submit a full report on my balancing work but as Mike is also working on this I decided to share the first part concerning the motor and motor pulley.
After removing the belt and just running the motor I could still detect a significant vibration. I continued by removing the motor pulley but the vibration was still present.
Looking up inside the “dome” at the top of the motor I could see something white, wobbling a little as the motor turned. Removing the dome revealed a plastic fan. I removed the fan and supported it axially on a light, horizontal tube as an initial balance test. This fan is clamped to the motor with a single screw and although it has a cutout this is presumably not intended to compensate for the weight of the screw, washers and nut. The first photograph shows an additional screw that I added (shown on the right side) as a counterweight. My original idea was to be able to first select an appropriate screw length and then adjust the position of the screw as a fine adjustment but it turned out that the fine adjustment wasn’t necessary. However, trial and error didn’t get me close enough, so inspired by the work of G. G.Kamysz (see CNC Milling Spindle @ DIESELRC.COM) I set up a small loudspeaker as a sensor and a reflective opto detector as an indexer for the position reference as shown by the second photo. The motor was removed from the mill and placed horizontally on rubber strips in order to allow it to vibrate freely.

THIS IS A DANGEROUS CONFIGURATION AND IS NOT RECOMMENDED!
The rotating pulley and fan were fully exposed while rotating at high speed . I was also very careful to switch the motor on and off only at the minimum speed setting because I was particularly concerned that fast deceleration caused by the brake could throw the motor off the table! Please don’t get hurt – either find a better, safer way to do this, or just forget it!

The third photo shows an example of what I saw on the oscilloscope. A peak in the waveform indicated the position of the excessive weight relative to the index pulse. Using this technique I was able to balance the fan end of the motor quite easily.
To balance the pulley end I drilled and tapped 3 pairs of M5 holes, 10mm deep at 120° separation in a pulley (I had ordered an additional set of pulleys because I needed an operational mill to machine the pulleys). The idea was to add grub screws as necessary in order to achieve the balance. My initial attempts with allen grub screws wasn’t very effective because these screws are essentially hollow and weren’t heavy enough. I therefore made some heavier grub screws by cutting the end off a couple of standard screws and making a small slot in one end. A combination of both types of screws was sufficient.
The end result was quite pleasing. With the motor and pulley re-mounted in the mill they now ran with very little vibration over the entire speed range.

While an oscilloscope may not be in everyone’s toolbox it might still be worth trying to balance the fan statically on a light plastic or thin walled alu tube.

In Part 2 (in a couple of days) I’ll describe what I found on the spindle end, and of course the all important results.

Step

[mike sr1]

I originally wanted to submit a full report on my balancing work but as Mike is also working on this I decided to share the first part concerning the motor and motor pulley.
After removing the belt and just running the motor I could still detect a significant vibration. I continued by removing the motor pulley but the vibration was still present.
Looking up inside the “dome” at the top of the motor I could see something white, wobbling a little as the motor turned. Removing the dome revealed a plastic fan. I removed the fan and supported it axially on a light, horizontal tube as an initial balance test. This fan is clamped to the motor with a single screw and although it has a cutout this is presumably not intended to compensate for the weight of the screw, washers and nut. The first photograph shows an additional screw that I added (shown on the right side) as a counterweight. My original idea was to be able to first select an appropriate screw length and then adjust the position of the screw as a fine adjustment but it turned out that the fine adjustment wasn’t necessary. However, trial and error didn’t get me close enough, so inspired by the work of G. G.Kamysz (see CNC Milling Spindle @ DIESELRC.COM) I set up a small loudspeaker as a sensor and a reflective opto detector as an indexer for the position reference as shown by the second photo. The motor was removed from the mill and placed horizontally on rubber strips in order to allow it to vibrate freely.

THIS IS A DANGEROUS CONFIGURATION AND IS NOT RECOMMENDED!
The rotating pulley and fan were fully exposed while rotating at high speed . I was also very careful to switch the motor on and off only at the minimum speed setting because I was particularly concerned that fast deceleration caused by the brake could throw the motor off the table! Please don’t get hurt – either find a better, safer way to do this, or just forget it!

The third photo shows an example of what I saw on the oscilloscope. A peak in the waveform indicated the position of the excessive weight relative to the index pulse. Using this technique I was able to balance the fan end of the motor quite easily.
To balance the pulley end I drilled and tapped 3 pairs of M5 holes, 10mm deep at 120° separation in a pulley (I had ordered an additional set of pulleys because I needed an operational mill to machine the pulleys). The idea was to add grub screws as necessary in order to achieve the balance. My initial attempts with allen grub screws wasn’t very effective because these screws are essentially hollow and weren’t heavy enough. I therefore made some heavier grub screws by cutting the end off a couple of standard screws and making a small slot in one end. A combination of both types of screws was sufficient.
The end result was quite pleasing. With the motor and pulley re-mounted in the mill they now ran with very little vibration over the entire speed range.

While an oscilloscope may not be in everyone’s toolbox it might still be worth trying to balance the fan statically on a light plastic or thin walled alu tube.

In Part 2 (in a couple of days) I’ll describe what I found on the spindle end, and of course the all important results.

Step

Step,
Carry on with the balanceing, I am very interested in your findings as well.
I used more crude methods on the pulley end, I located the heavy side then drilled and tapped it 1/4-28 and used grub screws to get it close, the fan end I havent had off yet, I was thinking about sending it out to a motor shop and having it done, but I dont want the machine down, so a bit of a quandry there ha!
I did loctite the motor pulley on to the shaft because unless its tight it will wear eventually and cause other problems.
Mine is good to about 4000 now, but needs to be better.
It is a 1750 motor and at the design rpm (name plate) it works fine.
I look forward to your findings..
mike sr

[Spinnetti]

I just got my machine setup, and don't know that much about how it "should" be, but noted that over 4000 it got loud.. would it be normal practice to take the motor with pulley and fan to a motor shop and have them balance? Rather have somebody with the right tools do it if possible... seems kind of odd it wouldn't be balanced for its rated speed ?

[philbur]

Machines do get louder as they go faster. No it is not normal practice to take the motor off and balance it. TurboStep is having fun but is possibly going a bit OTT.

One should take care not to develop a machine related hypochondria. Like its' medical relative, it can get very expensive for no real benefit. If you think you have an issue talk to Tormach, don't take everything you read on the Internet at face value.

Phil

I just got my machine setup, and don't know that much about how it "should" be, but noted that over 4000 it got loud.. would it be normal practice to take the motor with pulley and fan to a motor shop and have them balance? Rather have somebody with the right tools do it if possible... seems kind of odd it wouldn't be balanced for its rated speed ?

[philbur]

Is the motor not selected to be run with the VFD? Where did you find the design criteria for the motor maximum rpm?

Phil

PS: the rated rpm is not the design rpm.

It is a 1750 motor and at the design rpm it works fine, its the VFD that puts the rpm higher than its designed for.
mike sr

[SCzEngrgGroup]

It is a 1750 motor and at the design rpm it works fine, its the VFD that puts the rpm higher than its designed for.

You have no factual basis for making that statement, and I'm quite certain Tormach, being a company that does very thorough engineering on their products, would NEVER operate the motor outside its manufacturers maximum ratings. To do otherwise would expose them to a HUGE potential liability were one to fail at high speed. 1750 RPM is undoubtedly the *base* motor RPM, measured at a 60Hz frequency, which tells you absolutely NOTHING about its safe maximum RPM capability at higher frequencies. Inverter-rated motors are *designed* to be operated well above their base RPM, typically by 2-3X or even more. Were this not the case, there would be no reason for every inverter sold to be capable of running at least 120-200Hz or more.

Regards,
Ray L.

[mike sr1]

I took off the post in question as I sure dont want to start a war over it.

I will say that the Tormach does make a fine machine for the price period, and I love mine!

[riabma]

We are talking about the 1100, but what about the 770? Anybody has issues with unbalanced pulleys or similar?

I got this picture of the 770 in the Tormach site. The pulleys look like they are machined in aluminum instead cast iron like the 1100.


Ricardo

[philbur]

With 10,000 rpm max I think the 770 is a different kettle of fish. I believe specific balancing requirements where needed. Have a read in the 770 technical info, I think even the TTS had to be balanced for 10,000 rpm.

Phil

We are talking about the 1100, but what about the 770? Anybody has issues with unbalanced pulleys or similar?

I got this picture of the 770 in the Tormach site. The pulleys look like they are machined in aluminum instead cast iron like the 1100.


Ricardo

[TurboStep]

Spinnetti
If you just got your machine set up then you definitely don’t want to start worrying about problems that you may not even have, and which may not even bother you anyway.

Philbur
First of all, I’m not having fun at all. The finish I’m getting is, in my opinion below the real capabilities of the machine. Maybe I just have a Monday machine but other posters appear to be telling similar stories.
Am I going OTT? I’m just reporting what I’ve discovered and the results of my work. If someone else can benefit from this, then that’s what the forum is all about.

Riabma
Greg wrote “We balance the 770 which needs to run at 10,000 RPM, but we’ve never had a balance problem on the 1100 machine.” Which I guess answers your question.

The first results are promising but I still have some further testing. I’ll post the final results at the weekend – regardless of whether they turn out good or bad. Then I’ll just be a sitting duck and you can open fire (flame2)

Step

[David Bord]

Some great work on this thread! I love all the analysis and testing.

The motor fan looks like a pretty simple piece. Couldn’t you just machine a new one out of alum that could be designed so that it should require very little if no balancing?

Maybe to simplistic, but another thought is balancing the parts like you would RC helicopter blades or a motorcycle tire/rim with having the pulley sit on horizontal bar with low friction bearings? Spin and watch where the pull stops and add and remove weight till it doesn’t stop in same location.

How about chucking the pulley in a lathe and just trimming a tiny amount off the casting where the belt doesn’t ride, so the thickness is consistent. Have no idea if this would impact its strength though.

David

[btu44]

Turbostep,
Great idea for the poor mans piezo sensor. I think I'll give it a try when time allows.

Here is a short vid I did to find the RPMs to avoid during a finish cut.

PCNC1100 Spindle Vibration Test - YouTube

This is a vid of the deflection of the Z axis way. Granted this is a pretty heavy cut that would exaggerate deflection, but it still may have an effect on the surface finish.

[ame=http://www.youtube.com/watch?v=TeFR0ac0QoM&feature=plcp]PCNC1100 Vertical Colum Defelection During Heavy Cut - YouTube[/ame]

[TurboStep]

As promised, the second part of my “balancing act”.
First of all, thanks to Phil for his measurements. David suggested machining a new fan out of Alu. I thought of this as well, but only if the end results weren’t good enough. I can’t take credit for loudspeaker idea because this came from a paper written by Miklos Koncz http://www.zmne.hu/aarms/docs/Volume...pdf/12konc.pdf. His mechanical solution is much more refined and he also wrote software to evaluate the results using the parallel and game ports of a PC. While his system looks really interesting I just borrowed the sensor idea. One thing I didn’t mention is that the speaker cone is like a reference surface. It must remain stationary while the remainder of the speaker vibrates. I simply rested two fingers lightly on the cone, this turned out to be more than sufficient.

I had suspected the spindle pulley to be the largest contributor to the vibration due to the fact that I had measured a significant deviation in the thickness of the outer section and because it simply has much more mass at a larger radius than the motor pulley. To get a better idea of what was going on I decided to strip the paint. As I mentioned in an earlier post my pulley has a dent on one edge and it appears to have been painted twice: maybe once before the dent and again after?
Now, without the paint, the thickness deviation around the outer edge is 0.10mm. A hole had already been bored on the underside at approximately the same position as the thickest part of the wheel (first photo – the rust came after the paint was removed). I can’t say how accurate the resulting balance was, or whether it was balanced with, or without a key in the keyslot. The dent can be seen quite easily without the paint and with the edges beginning to rust (second photo). This pulley isn’t going back on my mill!
As I had never used the slow pulley position I initially contemplated removing the entire outer flange, just leaving the smaller section for the high-speed setting, but the first step was to try to balance it in the same manner as the motor.
I also had a new spindle pulley that was delivered with a total of 4 balance holes, each smaller than the hole in the original pulley, but all of the same size and depth. 3 were on one side and the fourth was approximately diametrically opposite. This means 2 holes would roughly cancel out. Again, I drilled and tapped 3 pairs of holes at 120° in this new pulley.
With the whole machine re-assembled I tried to improve the balance by adding grub screws as before. That wasn’t enough so I drilled out my threaded holes on the heavier side to twice the original depth. This wasn’t enough either! Then I noticed the hole in the spindle flange. This is the big “nut” supplied as part of the power drawbar kit that screws down onto the pulley. The hole for the set screw is quite deep and the set screw itself is short and hollow with a small brass plug at the end. I made a longer, solid set screw as described in my earlier post, which re-filled the hole (third photo – by the way, that’s a Fenner belt) and I was then able to achieve a balance.

It’s difficult to tell but I would say that the motor/spindle is less loud now (by no means quiet). I had intended to make before and after noise measurements but I forgot – and I’m not going back! Yesterday I was running a finishing cut at 5000RPM and realized that I could hear the stepper motors running. I don’t think I’ve heard them at these speeds since the Series 3 upgrade.

This whole thing is about finish quality and I can say that the improvement is significant. The 4th photo shows a before/after comparison at 5000 RPM (measured), 0.1mm depth of cut, same stock material and using the same 4 flute carbide end mill still mounted in the same tool holder. The wave effect is gone (the difference is more evident with the naked eye). Obviously there are tool marks but that’s not unexpected. Some have reported that the finish is acceptable at 4000 RPM or below. The 5th photo shows the same test but performed at 4000 RPM (measured). Although the wave effect isn’t very visible in the “before” sample the “after” result still better.
Probably the poorest finish that I have ever produced (on any mill) was on the chamfer shown in photo 6. This is a 2x2mm chamfer made in one pass with a ¼” Maritool Mill/Drill. Other than the fact that the first chamfer was on a 3 3/8” boss and the second (photo 7) was a straight edge they were reproduced under identical conditions. I would have liked to have shown the tool marks on the second image but they were so fine that I couldn’t photograph them. You will also notice the tool marks on the vertical face of the second photograph made by a 2 flute end mill. These marks correspond to the spindle frequency and indicate that I had some runout and was cutting with only one flute. I couldn’t expect the finish to be better than that!

I believe that face milling results are also better but I had previously removed my column shims to make sure that they weren’t affecting the rigidity of the machine, and after restoring them to the original values I still have a (very) small tramming problem. I’m not sure whether the tramming is very slightly worse than before or whether I wasn’t able to see it because of the vibrations. I would need to re-adjust the mill before I can deliver conclusive results but that’s not currently on the top of my priority list.

The TTS Set Screw holders have a balance dimple for speeds above 8000 RPM. When I compare the size of the screw on the fan and the hole in the drawbar spindle flange with the size if these dimples then I’m not surprised that I was getting measurable vibration at 5000 RPM. I was able to improve the total imbalance of the motor/pulley and the spindle/flange/pulley combinations by adding/removing weights to pulleys but it’s hard to say whether the pulleys themselves were really out of balance (they are balanced to some degree as supplied). I also only compared the finishes at the very end and I don’t have a comparison corresponding to just a balanced fan and spindle flange. This might be an interesting test for anyone who doesn’t want to go OTT like me!
At the moment I’m happy with the finish that my machine is now giving me so I’m not intending to make any further tests but I may conclude with a surface machining update after I’ve re-aligned the mill – that’s going to take me a while.

If anyone does attempt to replace the grub screw in the spindle flange then don’t do it the way I did! As I added screw-lock and tightened it down for the last time I could feel the spindle thread getting crunched. I guess I won’t be taking the flange off again in a hurry but a little piece of brass in there sure would have helped.

OK, fire away, I’m a sitting duck!

Step

[tbaker2500]

Excellent results! Thanks for posting such a detailed report. I'm glad to hear that this did help the finish. It'll probably help lots of other things last longer, too.

[mike sr1]

Turbostep,
you have a pm, I am not sure it went thru OK