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  #571  
Old Thu 04 December 2014, 20:43
KenC
Just call me: Ken
 
Klang
Malaysia
Not suspecting the PSU. higher V means higher top speed, which isn't you problem now.

The only thing you had not tried is tuning the AN882. Maybe this is where the issue lies.

I had the older tech MA860 to drive the 640oz-in Z-axis motor (direct drive 24T) with satisfactory performance on one coil. Parallel should give you a better chance.
Also, I'm pretty sure my Z-axis was heavier then yours.

Its nice to set all motors the same, but we all know that the operation conditions are very different for all axis.
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  #572  
Old Thu 04 December 2014, 21:25
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Ken, I spent a couple of hours last night tuning the AM882's with Protuner. They run more smoothly now (I did make other adjustments other than microstep and amps) but it made zero difference to the immediate stalling on the Z.

Like I said, I will deal with what I have now and when the money allows try different things. It is certainly an odd problem
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  #573  
Old Thu 04 December 2014, 21:28
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Oh, and I have had a thought to switch one of the motors to serial just as an excercise. Might still do that one day....
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  #574  
Old Thu 04 December 2014, 22:30
KenC
Just call me: Ken
 
Klang
Malaysia
Bruce, your problem triggers my curiosity... still can't stop thinking about it.
Maybe we could try other Zero $$$ solution.

Micro-stepping does affect the torque. as a rule of thumb (no exact but close enuf), full step->full torque. 1/2 step->1/2 torque, 1/4 steps->1/4torque, 1/8step->1/8 torque.
I don't go beyond 1/8 or 1/10 steps as diminishing returns.

What is your Z-acceleration? lowering the Acceleration does help a bit too.
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  #575  
Old Thu 04 December 2014, 22:54
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Good point there Ken.... might just go and set the Z to 1 or 2 step and see what happens. As for accel, I am metric and have it set to about 300 I think....
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  #576  
Old Thu 04 December 2014, 23:05
lonestaral
Just call me: Al #114
 
Isarn
Thailand
Send a message via Skype™ to lonestaral
Hey Bruce.

Just watched your jackhammer video.

I had a similar problem on my Z when I first tried it.
The gas spring was too strong.
I replaced it with some conventional springs.
If the power goes off the Z retracts upwards.

I sometimes get the pinion jumping out of engagement if the cutter is short and the Z travel is long.

Keep at it. It is usually something small that causes the problems.
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  #577  
Old Thu 04 December 2014, 23:15
KenC
Just call me: Ken
 
Klang
Malaysia
300 seem right. if you are not doing 3D carving, just 2D stuff, you can even live with 100~200. Every little bit helps. that is what I would think.
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  #578  
Old Thu 04 December 2014, 23:41
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Interesting Al, I'll try anything to improve things. What size springs did you use? I noticed Shopbot use springs too so you may be onto something
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  #579  
Old Fri 05 December 2014, 00:52
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Ken, don't do alot of 3d yet, just 2d. I have plans for a christmas pressie that will encompass 3d elements so I'll leave it at 300 for now.
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  #580  
Old Fri 05 December 2014, 06:18
2e0poz
Just call me: Paul
 
Swindon
United Kingdom
Bruce appologies i had the motors confused. I have some IME motors that are oddball with the steps that read the same way. No worries.
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  #581  
Old Fri 05 December 2014, 06:30
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Seems like 640 Oz/In is just not enough to meet Bruce's expectations on the Z axis - although it seems like it's fine on the other ones. While we can try little optimizations to squeeze more out of the motor, it's likely to still be finicky - that's not a very large cutter he's trying to plunge, and it's not even lifting the Y car off the rails.

So, we can either make the Z axis easier to move, or we can increase the motor torque. Seems that Bruce has exhausted options on the axis itself, and is almost through the electrical options on the torque.

Perhaps it's time to consider either a belt drive or a geared motor, just for that one axis. Maybe you could carefully crank out one of those MDF temporary belt drives and test it out.

With that said, I was just musing on how the geared OM 3.6 ratio motors are only rated at 352 Oz/In, but the motor itself appears to be a 310 Oz/In, which * 3.6 would be 1,100+ Oz/In (if you don't break the gearbox). However, the 3.6 ratio also affects which portion of the torque curve you are in when you're contacting the material.

Changing your accel settings, your max speed or perhaps even changing the height from which you are plunging might help. What happens if you set the Z speed much lower or higher? We want to try to use a different, stronger portion of the torque curve at the moment you hit the material.
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  #582  
Old Fri 05 December 2014, 12:11
pblackburn
Just call me: Pete #98
 
South-Central Pennsylvania
United States of America
Quote:
Originally Posted by bradm View Post
With that said, I was just musing on how the geared OM 3.6 ratio motors are only rated at 352 Oz/In, but the motor itself appears to be a 310 Oz/In, which * 3.6 would be 1,100+ Oz/In (if you don't break the gearbox). However, the 3.6 ratio also affects which portion of the torque curve you are in when you're contacting the material.
Brad, a similar situation with the PK296A2A-SG7.2 rated at 704 oz-in with a motor rated at 400 oz-in(at least according to tech support). Math doesn't add up. I think the limiting factor is the spline shaft they use and the cast gearbox.

Bruce, I would make a gear reduction for the Z. Something easy and quick to test and see what happens then. I know that mine will force itself out of the rack, I have done it many times by mistake, my motors are smaller than yours but are on a 4:1 reduction. Then you can decide how to approach a possible solution.
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  #583  
Old Fri 05 December 2014, 18:31
lonestaral
Just call me: Al #114
 
Isarn
Thailand
Send a message via Skype™ to lonestaral
The spring.

Wire diameter 2mm

Outside diameter 16mm

Length 600mm
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  #584  
Old Fri 05 December 2014, 20:18
KenC
Just call me: Ken
 
Klang
Malaysia
Gearbox torque rating as the name implies is the rated torque the gearbox can handle. I reckon the gears &/or other parts of the gearbox will not live long with higher torque even though it can produce more torque. The maths & figure do add-up, just that we don't understand them as much as we wish.
Stepper motor characteristic isn't linear & its inappropriate to scale them proportionally like we do with normal motors... its a lot more complicated then that.

IMHO, 30T is a very bad choice for Z-axis direct drive. I would use the smallest pinion which will still fit the stepper motor shaft. but AFAIK 23~24T is the smallest pinion with enough meat to hold stock Dia.12mm stepper motor shaft.

how about using MOD. 0.5 rack & pinion? maybe that will improve the mechanical ratio by a fair amount. without the cost of timing pulleys.
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  #585  
Old Fri 05 December 2014, 21:29
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Guys, first let me clarify what the video represents..... the minimal pressure to stall the axis. The spindle is off in the video. I could have just grabbed hold fo the Z and the same thing would have happened, spindle running or not. For example, the first dust shoe I made I thought the bristles were too stiff so I made another one with *really* soft bristles. Just tried to use that and as soon as the z compressed them a minute amount it stalled out. I *can* cut things, I just have to a) plunge really slowly and b) not plunge too deep and I can have no dust collection at this point.

My only immediate option is to make one 3:1 drive for the Z. I have to somehow enlarge the 8mm holes in the center of my 45T pulley to 12.7 and go get some 12.7 cold rolled steel rod. I *think* I can do the centre holes myself if I take about .25mm cut depth at a time. Oh, and I have all the pulleys for all the drives, 15T small with 12.7mm bores and 45T large with 8mm bores, plus 16mm wide belts.

My machine was built on a budget and now that budget is rearing it's ugly head. When some spare dollars make their way into my pocket I will be making a ballscrew Z and changing out all the motors for something else from somewhere else.
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  #586  
Old Sat 06 December 2014, 11:11
pblackburn
Just call me: Pete #98
 
South-Central Pennsylvania
United States of America
Wire it half coil in the different configs and try again. Make sure that one winding is not bad or open.
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  #587  
Old Sat 06 December 2014, 15:21
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Would grinding the 12.7 rod down to 8mm at one end to make a stepped shaft work?
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  #588  
Old Sat 06 December 2014, 17:49
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Making my 3:1 belt drive with what I have, that being 8mm hardened rod, a couple of 608zz bearings, a 20T pinion with an 8mm bore plus my 15T (12.7 for the stepper shaft) and 45T 8mm bore 16mm wide pulley. I am making the body out of 12mm acrylic, I did a test one out of 12mm MDF but it was too flimsy. I know 8mm rod isn't the greatest choice but should suffice for a short period.

That will at least let me test the belt drive theory and see if I need to replace the motors in the future.
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  #589  
Old Sun 07 December 2014, 21:58
KenC
Just call me: Ken
 
Klang
Malaysia
15T for 12.7 shaft? May I ask what timing belt/pulley you are using?
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  #590  
Old Sun 07 December 2014, 23:06
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Yup, T5 16mm Here: http://ausxmods.com.au/index.php?mai...products_id=25
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  #591  
Old Mon 08 December 2014, 15:58
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Well, I got my first 3:1 drive built out of MDF (stuffed up the acrylic one ) and am happy to report the Z will now crush the dust shoe and will jump out of the rack when the spindle hit the table. Better than it was by a long shot but I am still not overly happy with the motors.

Going to build a few more drives to the Y & X, again out of MDF until I can get some ali plate.
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  #592  
Old Mon 08 December 2014, 16:13
pblackburn
Just call me: Pete #98
 
South-Central Pennsylvania
United States of America
Good idea. I might recommend adding a thin piece of metal to sink the heat away from the motor between the motor and the wood. Wood will insulate the heat and make the motors retain heat. You will be surprised how much heat is transferred through the face.
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  #593  
Old Mon 08 December 2014, 20:43
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
The MDF is turning out to be a little flacky and am not overly impressed with my pulley selection. However I know it will work to cure some of my Z problems. I have decided to change to Ross's (SurfCNC) belt drives substituting HTD T5 pulleys and belts and currently have a request in to TEA for pricing on belts, pulleys and some 24T pinions.

In the meantime I will resurface my table with dust collection (now that I can) and then revert the Z back to standard and continue cutting without dust collection but not having to chase miniscule grub screws
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  #594  
Old Mon 08 December 2014, 21:21
KenC
Just call me: Ken
 
Klang
Malaysia
T5 belt seems big but it will work.
MDF is only good for short term fix. I would suggest properly seal the wood with a few coat of paint.
With 3:1 belt reduction, you can use your 30T is actually better than 24T.
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  #595  
Old Mon 08 December 2014, 21:33
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Hi Ken

Currently I am using T5 in 16mm wide belts and 15t with 45T T5 16mm pulleys. My current belt drive is a quicky using what I had lying around so I have 8mm shaft with 8mm ID 20T pinions. The only real problem at the moment is keeping the little biddy grub screws tight, M3 on the 15T and M4 on the 45T. I am using JR's design of drive and the motor sort of hangs out in the wind so to speak and the torque from the motor is flexing the 12mm MDF, hence me saying it was flimsy. The design was originally intended for 1/2" aluminium or on my case 12mm.

Switching to Ross's drives I am going up to 4:1 with 18T small and 72T big. The 72's will have M6 grub screws and the 18T have M4 grub screws. Deciding if I will get steel plates laser cut (depends on cost or quotes) or to make them out of 6 or 10mm aluminium
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  #596  
Old Mon 08 December 2014, 23:18
KenC
Just call me: Ken
 
Klang
Malaysia
Go for MS plates. 3mm thk is more then ample, actually 2mm would do. IF you are only making one set, you can hand fabricate with the use of holesaw & power grinder from scrap metal lying around..

I can't remember where & who came up with the "series" grub screw, i.e. one scrub screw in, with a second grub screw butting the end of the 1st. It worked for me. I also applied a good dash of loctite to be sure.

Spot welding the bearing to the MS plate may seem inappropriate engineering works. BUT it dirty & cheap fix & it works very well.

#PS, it is tempting to go for higher ratio than its required. so be careful with your choice. 3:1 with 30T is more then sufficient. for your case, reason, without belt reduction, your motor can hold the Z-axis inplace without external force. 3:1 reduction lighten the load to 1/3 which is very good service factor anytime of the day.

Last edited by KenC; Mon 08 December 2014 at 23:21..
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  #597  
Old Tue 09 December 2014, 04:17
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Thanks again Ken, you talk alot of sense. If I was to stick with 3:1 I would go 20T/60T just to get bigger grub screws I have a bit of time to think so will make a decision soon. As for what I have now, well I'll dig out my Loctite bottle and stick the little buggers in!
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  #598  
Old Wed 17 December 2014, 14:23
racedirector
Just call me: Bruce #122
 
New South Wales
Australia
Cut and assembled my 4 3:1 belt drives out of MDF and the results are satisfying. Chatter on curves has all but gone and the Z can actually push down on my dust shoe. Will go to the next level now and grab some 12mm aluminium, 1/2" bearings and 1/2" steel rod and make the real ones.

Also cut my T slots into the table (8x22mm slots in the 18mm bottom sheet, 8mm slots in the 16mm top sheet) [I know you said it was a bad idea Ken ] and now need to make clamps and knobs for hold downs plus a couple of jigs for doing special things.

Surfaced the table once again with dust collection and 13 minutes later was all ready to go. Marred my new work immediately by stuffing up a tool path and cut 12mm into the top, scarring it permanently. Oh well, all part of the process
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  #599  
Old Wed 17 December 2014, 14:34
pblackburn
Just call me: Pete #98
 
South-Central Pennsylvania
United States of America
An independent shoe that the spindle moves in and out of will take stress of the Z as well. Just takes a little work to create. Will give you a good seal to the table for fine dust collection.
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  #600  
Old Wed 17 December 2014, 14:40
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Bruce,
Fill that hole with some bondo and you are back in business!
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