7.2 Motor upgrade report

[fleinbach]

Well I finished my 7.2 upgrade and so far I am very impressed.

Now before I tell you the results I might add my significant improvement may not be totally from the 7.2 upgrade alone. While I was in the maintenance mode with wrenches out I also went over and tightened everything up. I most likely should have made some test cuts after just installing the 7.2 motors but I didn’t. So this is the results of the upgrade and complete adjustment to all moving parts of the Shopbot.

I used scrape pieces of ¾ MDF for the test. I cut 10” diameter circles from 12” X 12” scrape pieces. I used a ¼ inch Whiteside bit and cut full depth single pass at 8 ips. This was not a new bit but one I have used to cut 20 or more sheets of MDF. I might add this is some of the smallest pieces of material I have cut using my 7.5 HP vacuum system and it held them perfectly in place throughout the cut.

I have absolutely no chatter marks whatsoever. I cut both clockwise and counterclockwise single path cuts with a well used bit.





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The circle I cut clockwise was .025 larger then it's intended 9.75" size. Pictured below is the reading of the circle I cut counterclockwise using my new digital calipers from Harbour Freight. It was .0465 smaller then it's intended size should have been.


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Close up of edge

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[paco]

I have made the same upgrade but without further tweak or maintenance. Maybe just added more grease that's all. It's been a week now and I'm very happy.


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This is a 2 inches tall letter cut out from 1/8" acrylics with no changes from the way I was cutting it before the upgrade. This is as close I can get with the macro on my camera; about 4-5 inches. From what I've seen before and apart from the kerf width, it is very comparable to laser cut.

I don't have pictures but cutting 2 inches thick HDU in a single pass was just as very smooth; read no chatter.

The upgrade was easy to do; thanks to SB for putting "everything" I needed in the boxes (I could have used pieces of shrink wrap tube) and to Frank L. for the VU specs. that I just need to copy and paste from the forum.


One thing I'm wondering about; should I play with the V.Fil as I did with the 1:1 alpha. Setting it from A to 8 or such?

[fleinbach]

Paco,

I also would like to know if there is any advantage to resetting V.fil but if I remember correctly I believe I read a post where Brady said it did not work to make the change for the 7.2 motor upgrade.

There was one Change I did make though that I have not seen mentioned anywhere. I adjusted my spring tension to 6 full turns. With the old 2 1/2 turns I noticed it did not take much pressure to cause the motor to move when pulling against it. After adding the extra turns they hold far better.

[Brady Watson]

Frank,
You can set the VFil to a max of 8 on the 7.2:1 motors. You will notice an immediate increase in motor smoothness. I have mine at 8, but anywhere in the 6 to 8 range on the dial is good.

-B

[kasey_jones]

What is V.fil?

[fleinbach]

Kasey,

V.fil is a pot adjustment on your motor controller boards. Here is a link were Brady describes changing it for additional smoothness. http://www.talkshopbot.com/forum/show.cgi?tpc=26&post=52650#POST52650

Brady,

I checked and they were set at 6 from the factory. I will try setting to 8 and see if I notice any difference but things seem pretty smooth right now where they are. Although I did notice when cutting the circles all the way through it sounded very smooth but at the end of the cut there is a Thunk sound. It seems like there is no ramp slow down at the end of the cut path. Instead it’s more like it comes to an abrupt stop from 8 ips. I also tried air cuts at up to 12ips and the faster it is going the worse the sound is at the end.

[Brady Watson]

Frank,
The V.Fil setting is analogous to mid-band resonance adjustment on Gecko drives. All steppers show some mid-range resonance, regardless of make. While it definately smooths out the motor note, I'm not sure exactly how much smoothness it gives you over the lower V.Fil settings. You might find that adjusting your ramps, particularly slow corner speed, is beneficial in soaking up any abrupt movements. Setting your ramps to .1 or .2 all the way down the list sometimes results in rough movement. For very fine jobs, like cutting 3D with a 1/32" ball etc, I put the ramps back to .4 all the way down the list, and turn down the slow corner speed. While the tool doesn't move as quickly as it could, it does result in a much smoother cut...which is what I am always after.

-B

[harold_weber]

Frank, I think I can see visible marks on the MDF in your photo titled "close up of edge". If they are really there, what do you think is the cause - could their spacing be equal to the rack gear teeth pitch?

[fleinbach]

Harold,

Yes there is a very slight trace of tool marks but but they are an improvement over my previous setup before the upgrade. This was not the best test one could make since I only made my test at 8ips single path. Until I make more cuts at differant speeds I can't say what I might find.

Brady,

I nearly always prefer quality over speed so I will leave my ramps at.4 as they are. The default for slow corner speeds is set at 65. How much slower would be a good place to try?

[kasey_jones]

Frank -

Followed the link and changed the V.Fil as mentioned by Brandy. WOW! S-m-o-o-t-h! Any other tweaks I can take advantage of??

Thanks,
Kasey

[Brady Watson]

Frank,
I rarely set the slow corner speed any more than 50. I really boils down to the shape of your parts, if the strategy is 2D or 3D and how hard you are pushing the tool.

I like to set up my machine so that I never encounter banging at the extent of a raster, or abrupt movement in any axes, especially the Z. The gantry that you and I have is relatively light weight and you can't throw it around all over the table and expect not to get even a little bit of vibration. For production 2D cutting I'll set the slow corner speed in the 35 to 50 range. For general 3D cutting, most of the time I will leave it on 40. If using a very small bit or the 3D relief has a lot of straight walls to it where the Z could 'bang', I set the slow corner speed down to like 30 & observe how it traverses long sweeping features of the model in addition to the flat upward movement of the Z when it encounters a wall. I often adjust ramps in the middle of a file with settings that I feel are ideal for the parts at hand. Some jobs NEED the slow corner speed pushed down to 20 to reduce cutter debounce on 3D reliefs when using .015 to .0625" ball cutters with tight stepovers.

While SB does setup default VR when you install SB3, I find that it is impossible to have a set of parameters that fits everybody's needs. I used to just adjust ramps once in a while when cutting and leave that setting for a few months etc. Now I find myself fine tuning the ramps on almost any job that I feel would benefit from a few tweaks here and there.

-B

[fleinbach]

Thanks for the info Brady, I will try playing with the settings. I'm looking forword to actualy cutting some real parts since the upgrade hopefuly later this week. From what I have seen so far I beleive I will like making the change.

[Brady Watson]

Frank,
You're gonna love it!


After about 18 months of running this setup, I'm still really pleased with the machine. It's what I always wished the PRT would have been from day one. It took a little while to get to this point, but it's a totally reliable and smooth running machine. In those 18 months, this machine has cut over 250,000 parts, both large and small in just about every material you can think of.

-B