#211
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Ries,
never apologize for asking questions, you are correct in the respect that the bearings are wider than the metal plates the plates are 1/4 inch thick and the bearings are a little more than 3/8 inch thick if I remember correctly, and it is also because the MM motor plates already have a hole cut in them way bigger than the bearing, also the bearing boss requires machining to fit the bearing correctly and it is easier to machine a small part in the lathe than a large plate, I suppose you could use a flange bearing but most of them are really poor in quality, and with the bearing boss the bearing is supported correctly, do it right the first time and you wont have to do it again, at least that is the way I look at it... //chopper |
#212
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Quote:
thanks for the explanation, all clear now! With your permission, I would like to take your plane and build my own next year based on your design. Ries |
#213
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Ries,
these plans are here for all to use, use them change them what ever you want to do that is why I posted them, //chopper |
#214
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Have you built a tranny with these plates yet? I would like to see pics of it.
Does it use the same bearings,gears and belts? |
#215
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it is just a cosmetic change all the parts are the same,
//chopper |
#216
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So just so I am following (I am slow ) . The belt drive plate is the same but is rounded off for laser/plasma cutting.
The Z plate is a Moded M510312PB swing plate? Could I just mod M510312PB plate and the M510322PC motor plate to take the gears and shafts with regular bearings? ie take out the large holes? Also would it be possible to use the stand off "posts" (4 of them) to join the plates instead of welding them? This way all of it could be screwed together. |
#217
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Mike,
the plates are basically the same it is just mostly cosmetic.. you are correct the Z plate is modified, from the stock MM plate the only reason for this is to eliminate the funky bends on the Z spacer plates... go back in this post and look at the Z drive plate pictures, you will see what I mean http://www.mechmate.com/forums/attac...=1&d=124814485 the roundness is to guard the pulleys from fingers etc. getting into them, and to make it easier if someone wanted to build covers for the drives to keep out dirt etc. you could use stand off posts if you like, I did not design for them I feel that the welding makes a much stiffer part than bolting, bolts can move welds do not, also it is harder to fit the 72 tooth pulleys in the space if it is bolted together, so you may not get the 4 to 1 ratio,( I believe that the 4 to 1 ratio with the 20 tooth pinion is the optimal resolution) you could take out the large holes if you want and re-size them for bearings, this is why I used the bosses since the bearings I used are .375 wide and the plate is .250 wide you wont get the proper support for the bearing, and if the fit is to tight the bearing will bind, to loose it will fall out, I also built them to be used with the stock MM motor plates since they are included with all the laser kits, why not use what you already have, that way I thought it would be an easy transition to the belt drives, if some one decided later on to go to them like I did, Mike feel free to modify change alter redesign, etc..etc.. you just might come across a great design in the process, I am just sharing what I have done, I am sure someone can improve it,... //chopper Last edited by chopper; Tue 24 November 2009 at 17:06.. |
#218
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Mike,
I also wanted to add that the bearing bosses (cups) were designed to fit into the holes cut into the existing motor plates that is why there is a shoulder on them and they are machined to fit into them..hope this make sense to you //chopper |
#219
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Here is the plate with tabs. How long would they need to be to allow for bends?
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#220
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Mike,
the wings should be 2.250 in length if you use the same pulleys that I did (width) and you use the longer bearing boss on the motor side.. //chopper |
#221
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Chopper I noticed you're using the Kreling motors. Do you have the model number for them? Also what size and brand of rack and pinion gear are you using? I would like my machine to work as well as yours!
Thanks! |
#222
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swatkins,
I am running the kelling 450 ozin motors # KL34H260-60-4A (remember that the 450 ozin is mutiplied by 4 with the transmissions so the end torque is 1800 ozin) the following are the parts for the belt drives stock drive,http://sdp-si.com the 72 tooth pulley is part number A6A3-72NF03716 @ 31.97 each the 18 tooth pulley is part number A6A3-18H3716 @ 10.98 each the belt is a 200xl with Kevlar reinforcement part number A6B3-080037 @ 7.61 each the rack and pinion are from mc master-carr www.mcmaster.com/ and the pinion is a 20 tooth, the rack and pinion are as per the plans if I remember correctly it is a diametrical pitch of 20, and 20 degree tooth angle you need to check with the plans to make sure... the reason I run the 20 tooth pinion is the smaller pinions do not magnify back lash issues, the larger the pinion the more magnification of back lash also the smaller the pinion the more resolution that is gained, (others may disagree with this this is just my findings) if you want your machine to cut as well as mine you will need to take your time and be patient as you build, and pay attention to detail I have also made a few modifications to my machine nothing to significant, but it seems to work, check out my build here http://www.mechmate.com/forums/showthread.php?t=1951 hope this helps... //chopper Last edited by chopper; Thu 07 January 2010 at 13:54.. |
#223
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Quote:
I was going to build this machine and then a smaller one for metal cutting but after seeing the results you are having I think a single MechMate will take care of almost all my needs! You posted a link for the bits you were using for metal. I was having trouble bringing up the series you suggested on their site... Would you happen to have the part numbers for your favorite metal cutting bits handy? Light steel and thicker aluminum will be the metals I use most as I am hoping to use this machine in place of my mill drill in most cases... Thanks for all your help ! Steve |
#224
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Oh this is so exciting ( and expensive!) I just ordered the motors and now I am looking for the correct rack and pinion....
The McMaster-Carr page you linked to only had 3/8" wide racks.. Looking around I found this page that had 1/2" wide , 20 degree and 20 pressure angle items... The 20 tooth pinion also was large enough to bore 1/2" where the one on the other page would only allow 3/8" shaft size... Do these items seem familiar ? 5172T12 Steel 20 Deg Pressure Angle Spur Gear 20 Pitch, 20 Teeth, 1" Pitch Dia, 1/2" Bore In stock at $16.76 Each 5174T21 Steel 20 Deg Pressure Angle Spur Gear Rack 20 Pitch, 1/2" Face Width, 1/2" Height, 6' Length In stock at $46.50 Each Thanks Steve |
#225
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One of the reasons a MechMate cuts well is because the gantry has a great deal of mass.
It may be counterintuitive, but if you want to cut aluminum, make it big. |
#226
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These guys are cheaper than McMaster for racks.
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#227
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Quote:
Thanks for the link... There are no prices on their website so I am going to send them an email... How much better are their prices? Steve |
#228
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Steve,
the bits that were listed were onsrud look at their web site and search for high speed metal cutting bits, the actual bits I used were from a local supplier that has a house brand mill with the proper coatings for stainless steel, if I were you I would look for a local machine shop supplier they should have the bits you need and more than likely cheaper than onsrud, then you can experiment with different flutes and coatings...and get them locally..also the slower you can get your router/spindle to spin the better off you will be for metal cutting... //chopper Last edited by chopper; Thu 07 January 2010 at 16:37.. |
#229
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Is there a 'zero backlash' timing belt&pulley
Chopper (or anyone else who knows)
Is there such a thing as 'zero backlash' timing belt&pulley? I saw you use 0.2'' pitch, which translates to about 5mm. Is it plain timing belt & pulley? clearly you get no backlash. I intend to use quite harsh acceleration values - would you say that regular timing pulley, made of aluminum, with 0.375'' (9mm) kevlar reinforced belts will give a backlash free machine for years to come, or would you recommend steel pulleys? maybe .625'' belt? What say you? |
#231
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:) nice closure?
You must admit it is funny in some way (the shared IP of Jimbo & Chopper). shows enthusiasm .
Gerald, as probably the person who was involved in every debate on this forum, and quite a few on others, please do advise. maybe as a nice closure to the loud tones this thread experienced: I have backlash. no lost steps, always manage to get back to the exact same locations, only that there is a 'play'. I grab the gantry in my right hand (the strong one), and I am able to get a 1mm movement when moving by hand back and forth. this is quite a problem. if I always cut the same direction, I'm able to get by with perfect cuts. if I change direction on the same cut in a different cut level, the backlash shows, you see a stair on the material. I also cut decorative panels (when will sales pick up...), and then it becomes a major problem. I want to cancel the backlash, and from threads around here I learned that the timing belt and pulley is a solution, and a great one. I also have now SG7.2 geared oriental motors, want to change to keling 906oz-in with 3.6 ratio belt (20-72 teeth). 1. will the timing solution do? I have very high acceleration values. 2. one of the sales people here told me there is such a thing as 'zero backlash' in timing pulleys & belts, did anyone hear of it? 3. isn't it better to use steel pulleys rather than aluminum? I mean aluminum is prone to develop backlash due to high accel, isn't it? on extreme take a hammer, slam steel, slam aluminum.... you get me. 4. any advice on solving backlash? definitely the gear is the problem. didn't employ the machine too much, yet already I have meaningful backlash. you can hear the gear slam as you rock the machine while idle. peace! |
#232
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You talk of very high accel values in your case, but I don't believe they can be very high because the stepper motor would lose steps (slip). Your torque/force/impact limit is set by the stepper motor's magnet field strength. Everybody increases their accel values until the stepper motors cannot handle it, and then back a bit......therefore I believe there is nothing special about your application and you can use the same belt drives as everyone else.
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#233
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would you say plain timing belt & pulley setup will do the trick and solve the backlash issues? this is what remains unknown to me, because of all the discussions I already read, I haven't a firm understanding if that is it. Does it do the trick?
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#234
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Orotemo, if, in fact you have a sloppy set of gearboxes with backlash, then the belt drives should help you to eliminate the backlash.
Will eliminating that backlash solve your cutting issue? That is harder to be sure of. There are two things that I would check before spending a lot of money. Both of them should be checked during your test of pulling on the gantry. The first is to make sure that your pinions are fully engaging the rack, and stay fully engaged. The second is that the pinion gear isn't sliding on the motor shaft. Based on your description above of hearing the gears slam around, it does sound quite possible that your gearboxes are bad. There seem to be a lot of people for whom the OM gearboxes aren't a problem, so it might be worth checking with OM; maybe they'll replace them. Have you always had the problem, or did it develop over time? |
#235
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I had a similar issue early on with my belt drives, I tried to get away with small grub screws and the pinions came loose and i could move the gantry a millimeter or two. After changing to bigger grubs screw i haven't had the issue again. So i agree with the others, a belt drive won't solve your backlash issue if your motors are in good order.
But to answer your earlier questions, if you do go for a belt drive, i wouldn't worry about a steel pulley, aluminium is fine. I went with a 16mm wide pulley just to give me a bit more margin but many people seem to run 10mm (3/8") without any issues. |
#236
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I have been playing around with a design based on choppers info here. One thing i noticed is that he claimed he used a 200xl belt with a 18T & 72T pulleys. His drawing shows a centre distance of 3.125". This doesn't work out. I put more trust in his measurement of centre distance than the belt number, so i assume he actually used a 160xl belt. This gives a theoretical centre distance of 76.49mm (~3.01"). But this means he only had 4 teeth on contact, not 5. I know he said he didn't have any issues but i think this is too far outside the recommended engagement and may cause premature belt failure. I'm working on a design that uses a 170xl belt to give 5 teeth in contact. not a big change to the design but gives 25% increase contact area. Will post some concept pics soon.
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#237
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We have found that the most common source of "backlash" seen in the x and y direction is caused by a loose z-slide. The z-slide roller eccentrics should be adjusted up to hold a pre-load on the z-slide. The z-slide should not wobble side to side.
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#238
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With the steppers energized, I can get .4mm of movement (entirely gearbox movement - I can feel the pinion rotate) in my y axis. For reasons of which I'm not entirely certain, I have much less in my X axis.
my z-slide is quite rigid. When doing things like cutting signs, this hasn't proven to be a problem. It only becomes a problem when I try to do inlay-type work. I'm able to work around this with backlash compensation, but my next machine will have timing belts. |
#239
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why wait for your next machine? you can retrofit belt drives...
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#240
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I have copied the posts regarding excessive backlash in the OM geared motors to Backlash in the gearhead of the Oriental Motor PK296A2A-SG7.2
This thread has been re-titled to focus on building your own belt-drive. I took the 4:1 out of the title because that may not be the "ultimate" ratio . . . . there is no such thing as the ultimate ratio in this case. Edit: This thread also now merged with the original "Build your own" thread. |
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