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Message |
    
Mike Richards
Registered
Username: Richards
Post Number: 27
Registered: 05-2006
| | Posted on Thursday, August 24, 2006 - 06:53 pm: | 
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This is Version 4 of my 3:1 belt-driven gearbox. It takes me forever to design something that I like enough to keep.
This version is cut from 1/2-inch thick polycarbonate. The spacers are 1-inch aluminum. (The extra-long shaft and rusty gear are left-overs from other projects.)
Starting at the shaft, there is a 1/2-inch clamp collar, #9 rubber O-ring, 1/2-inch shielded ball bearing, motor plate, 60-tooth XL gear, main plate, 1/2-inch shielded ball bearing, #9 rubber O-ring, 1/2-inch clamp collar, 20-tooth, 20-pitch, 20-degree spur gear. The aluminum spacers are 1-1/2-inch high, threaded for 1/4-20 machine screws. There is a 20-tooth XL gear bored out to 14mm to fit the Alpha stepper motor. The belt is a 150XL037. The original 3/8-inch mounting bolt was replaced with a longer 3/8-inch bolt, due to the extra thickness of the polycarbonate. The motor mounting bolts are 1/4-20 X 1-inch socket head bolts (so that the belt can easily be adjusted from the rear of the motor).
This version took about 1.5 hours to cut (Y-axis, 2 X-axis, no Z-axis) using a 1/4-inch O-flute cutter at 1.25-ips. Machining the spacers took forever. (Whatever made me think that using a metal mini-lathe would be fun? Can you say one full day machining and threading spacers?)
The 3:1 gear reduction on the X and Y axes reduced the normal Alpha 'chatter' problem enough that I can accept the occasional 'chatter' mark. Torque is 3X greater. Ted, at Shopbot, suggested that I try setting the Alpha drivers to 500 steps per revolution, rather than the default 1,000 steps per revolution so that the factory software/controller could supply pulses fast enough for a 3:1 reduction. The resolution on either 500 or 1,000 steps per revolution were nearly identical. In fact, the 500 steps per revolution setting seemed to produce smoother edges in the majority of cuts. It seems that the reverse should be true, but the proof is in the cut. I'm beginning to think that the increased torque is the main factor in getting better cuts. It might just be possible that the 3X increase in torque holds the 'inactive' axes in position so that they're not shoved around by the active axis.
I would have used higher reduction, but that would require a multi-stage unit - which would have been fairly bulky. The 20-tooth XL gear is the smallest that can be bored to fit the 14mm shaft on the Alpha stepper motor (according to W. W. Grainger's catalog). The 60-tooth XL gear fits better than the maximum size 72-tooth XL gear.
In any case, the 3:1 unit really helps with cut quality. |
Evan Curtis
Registered
Username: Evan
Post Number: 9
Registered: 12-2005
| | Posted on Thursday, August 24, 2006 - 10:34 pm: |
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Mike,
Nicely done! How is the unit tensioned up to the rack? The same as the Stepper was, with spring and turnbuckle?
Thanks |
Sheldon Dingwall
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Username: Sheldon_dingwall
Post Number: 5
Registered: 08-2006
| | Posted on Friday, August 25, 2006 - 01:59 am: |
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Very nice Mike. I wonder if the belt has any smoothing effect on the step marks? |
Mike Richards
Registered
Username: Richards
Post Number: 28
Registered: 05-2006
| | Posted on Friday, August 25, 2006 - 06:34 am: |
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Evan,
The motor can be adjusted vertically about 1/2-inch, which is more than enough to adjust the tension on the belt. The spring and turnbuckle are still used, except that I used 4-turns rather than the 3-1/2-turns recommended by Shopbot.
Sheldon,
The belt is pretty tight. Actually, it is tighter than I would normally run a belt - only about 1/8-inch deflection when tightened. However, it could be that the natural 'softening' of the belt helps cut down the 'chatter'. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 205
Registered: 11-2005
| | Posted on Friday, August 25, 2006 - 06:49 am: |
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Nice job Mike!
Any comment on how it stands up to sawdust? |
Mike Richards
Registered
Username: Richards
Post Number: 29
Registered: 05-2006
| | Posted on Friday, August 25, 2006 - 07:01 am: |
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Gerald,
In my shop, I've mounted a sign stating, "Only 'anti-cling' sawdust is allowed". Because of that sign, I don't have to worry about sawdust collecting on the belt and gears.
Seriously, sawdust hasn't been a problem. After every sheet, I customarily sweep the table and blow off the gears, rails, and motors. So far, there hasn't been any problem of any kind with sawdust. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 206
Registered: 11-2005
| | Posted on Friday, August 25, 2006 - 07:43 am: |
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"I'm beginning to think that the increased torque is the main factor in getting better cuts. It might just be possible that the 3X increase in torque holds the 'inactive' axes in position so that they're not shoved around by the active axis." I totally support this theory. I believe that a stepper motor cannot "hold" a micro-step. It will hold a full step, and even so, with some "spongy-ness". I plan to clamp a stepper in a vice, put a 2foot long lever arm on the shaft, and then feel by hand how a stepper actually steps, micro-steps and holds.
Good news on the dust. An open casing is probably better than a closed box. |
Mike John
Registered
Username: Mikejohn
Post Number: 53
Registered: 12-2005
| | Posted on Friday, August 25, 2006 - 07:55 am: |
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Mike
Can you send me the file to make that sign for my workshop,please?
..............Mike, the other one!(or is he the other one?) |
Gerald_D
Registered
Username: Gerald_d
Post Number: 207
Registered: 11-2005
| | Posted on Friday, August 25, 2006 - 08:16 am: |
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Your sawdust doesn't understand English |
Mike John
Registered
Username: Mikejohn
Post Number: 54
Registered: 12-2005
| | Posted on Friday, August 25, 2006 - 10:36 am: |
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Drat! foiled again!
Hang on! Does anyone from Utah speak real English? 
............Mike |
Gerald_D
Registered
Username: Gerald_d
Post Number: 208
Registered: 11-2005
| | Posted on Friday, August 25, 2006 - 12:28 pm: |
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Yes, the sawdust does. |
Mike John
Registered
Username: Mikejohn
Post Number: 55
Registered: 12-2005
| | Posted on Friday, August 25, 2006 - 01:34 pm: |
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Now that is true, as the trees were probably planted back in colonial days! |
Mike Richards
Registered
Username: Richards
Post Number: 30
Registered: 05-2006
| | Posted on Friday, August 25, 2006 - 02:53 pm: |
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Mike J,
English? Never heard of it! Here in Utah, we speak American - when we're speaking to outsiders. Among ourselves, we speak the pure Adamic language.
Gerald,
One of my concerns a few months ago was reduced current holding torque on stepper motors. It seemed to me then that as soon as an inactive motor went into standby mode (automatic reduced current mode to reduce motor heating), that axis basically lost almost all of its holding power, meaning that that axis could be pushed around by the active axis. My thought back then was to have Ted modify the Shopbot code so that whenever any axis became active, the other axes would move one step CW and then one step CCW continuously to keep all axes active (full holding torque).
I think that holding torque while motionless is the biggest argument in favor of servo motors. If I understand the concept of servo vs stepper, the servo motor/driver consumes almost no power when stopped, but instantly goes to as much power as necessary to resist movement - meaning that a servo motor can't be shoved around like a stepper motor. Of course there are significant factors favoring steppers over servos, but, if we have to use gear boxes to make a stepper work properly, why not go the full distance, install servos w/gearboxes and encoders (at 1/3 the cost of the Oriental Alpha stepper/driver)? |
Gerald_D
Registered
Username: Gerald_d
Post Number: 210
Registered: 11-2005
| | Posted on Friday, August 25, 2006 - 02:57 pm: |
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And Adam spake to Eve: "...with what router shall we smite the apple tree?" |
David Rosenbleeth
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Username: Dave_r
Post Number: 10
Registered: 07-2006
| | Posted on Saturday, August 26, 2006 - 01:09 am: |
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"You're in luck if you gotta a McCullogh chain saw"
Moral of the story: If you wish to smite the tree-use a saw; to carve it use a spindle and Geckos.
Been cutting parts with the Agek rig for a while now and my guys still have nothin but smiles.
Dave |
Joe Crumley
Registered
Username: Joe_crumley
Post Number: 10
Registered: 07-2006
| | Posted on Saturday, August 26, 2006 - 03:15 am: |
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David,
Could we see some of these parts? I allways enjoy seeing products made with a router. |
Mike Richards
Registered
Username: Richards
Post Number: 34
Registered: 05-2006
| | Posted on Thursday, September 07, 2006 - 11:08 pm: |
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Here's the 3:1 ratio belt-driven-transmission cut out of aluminum on my Alpha.
Cutting speeds in the 1/2-inch thick 6061 aluminum were 0.60-ips XY-axes, 0.05-ips Z-axis, 12,000 RPM, 0.075-inch step down per pass, using a HSS 3/8-inch cutter designed especially for cutting aluminum. Those speeds required flooding the cutter with tapping fluid made especially for aluminum. If you look carefully, you'll see some edge marking in various places. That was caused by letting the cutter get too dry (thus getting too hot).
After using the 3:1 ratio for several weeks, it seems to work perfectly for the kind of work that I do. There hasn't been any problem with 'chatter'. The open frame has not been a problem - no dust on the belt or gears. In short, with the 3:1 transmission, my Alpha is cutting like a real CNC router. |
Michael Cunningham
Registered
Username: Deviousmw
Post Number: 2
Registered: 03-2007
| | Posted on Tuesday, March 20, 2007 - 05:37 am: |
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Does anyone have a set of cad drawings to build a belt/gear reduction box.. maybe a list of parts? I need to build two belt reduction units for my nema 34 steppers.. say 3 or 4 to 1 reduction. I however an a complete noob at this with no lathe or mill. Something very similar to the ones shown here. Suggestions? Ideas? Plans? Does the metal kit have provisions for making belt gearboxes?
Does anyone make these on the side for people?
Thanks,
DeviousMW |
Greg
Registered
Username: Greolt
Post Number: 17
Registered: 08-2006
| | Posted on Tuesday, March 20, 2007 - 01:20 pm: |
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Michael
These are a couple of pics just to give you more ideas.
I don't have any drawings. And this is obviously not a mechmate.
Same principals apply though. Keep the relationship between the pivot and the pinion shaft no more than 45 degrees from horizontal. I would make it less if I was starting again.
I see the weak point of other designs to be the pivot mechanism. Any slop here goes straight to backlash.
Whenever I drill a hole and put a bolt or shaft through it, it usually ends up with about 3 to 5 thou slop. Then the rapid back and forth of the axis will increase this with wear.
That's why I put bearings on the pivot and made them a firm fit in their housing and on the shaft.
Also be careful in your belt selection. Mine are T5 and the "cog" on the belt is smaller than the "groove" on the pulley.
So far this has not showed up in accuracy but this is not a good place to start.
 |
Michael Cunningham
Registered
Username: Deviousmw
Post Number: 3
Registered: 03-2007
| | Posted on Tuesday, March 20, 2007 - 10:46 pm: |
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Greg,
Thanks for the info.. couple more questions..
On you pivot point I see you have a press fit bearing on each side of the shaft. What keeps
the shaft in place? Is there some sort of clips I dont see? Same question on the other shaft as well. Where did you get your gears from? How do you keep the large gear in line with the smaller one. Again another clip? Interested in making another set of these for some extra cash?
Thanks,
Mike |
Driving Mechanisms: Rack/pinion, gears, screws & chains