High temperature timing belt
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@deckingman my moving mass is 25kg and I'll aim for highest possible accel. I use nema 34 clearpath servo.
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@kuon Given that mass and the temperature you are aiming for, are you sure belt drive is the best option? Have you explored other alternatives such as for example rack and pinion (sometimes called spur gears)? Lead screws of the required length might be hard to source for a large machine, but racks can be bolted together to make almost any length and they would withstand the temperature (although you might have to allow for thermal expansion).
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@deckingman I actually have a design with rack gears, but it requires moving motors and some axis requires multiple motors that have to be synced. Belts let me have one motor per X and Y axis. For such a large machine I though having direct mechanical coupling was better because if motors unsync for any reason it could cause major damage.
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@kuon OK, so it's back to belts. But why have dismissed the 12mm wide Gates belt that was suggested? We know the mass is 25Kgs but you haven't specified what acceleration you want. Force = mass x acceleration and if you don't know the acceleration, you can't calculate the force. So what calculations did you perform when looking at the specifications for the gates belts which made you dismiss them?
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@deckingman I used 1g as max accel as it gives plenty of margin over the accel I am going to use. At 1g, it's 250N, with a 20mm diameter pulley, it's 2.5N/m torque and 1500RPM for 500mm/s max speed, which is about 400W (for some reason, most belt sizing guide I found from manufacturer uses watt or HP), and for this gates recommend 25mm wide belts. I also did the math in the gates belt sizing guide.
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@kuon run multiple 12mm belts side by side?
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@mendenmh Yeah that's one possibility, but that's more hassle for tensioning and such.
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@kuon So as has been suggested, use two belts. Or settle for 5,000 mm/sec^2. You did say that this is to be a printer, so that acceleration would only be useable for non-print moves.
Edit. Also, I'm struggling to understand how you've got the mass up to 25Kgs. When I used my 6 input hot ends, with 6 extruders mounted on a second gantry, the total moving mass was around 5 Kgs. That's two gantries, each with two X rails around 600 mm long, carrying a large, 6 input, liquid cooled hot end plus 6 extruders with motors, plus assorted fans and two expansion boards yet the moving mass was one fifth of what you have. Can't you reuce the mass from a whopping 25 Kgs?
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@deckingman the head is large because the gantry is 1200mm and there is a pellet extruder and a laser on the head. We are working on a technique that improve strenght and smooth the surface with a laser after extrusion. The weight is the head + gantry + water cooling + motors to manipulate the extruders and laser (small "mini axis"). The extruder alone is already 7kg. We have a working prototype of a smaller machine on which we use regular belts with a normal fdm extruder and much lighter gantry. We use high accel for laser moves.
As a side note, GT2 12mm wide seems to require custom made pulley. I cannot find off the shelf clamping pulley larger than 9mm wide for 2mm pitch. I use mostly McMaster and misumi. I found some chinese pulleys on ebay and alibaba but they are all set screw.
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@kuon You said in your OP that you had found a belt but that it was 8mm pitch. I'm guessing that 8mm won't give you the resolution you need. So how about using that belt with 4:1 pulley sizes which would then give you the resolution of 2mm pitch belts. Plus the gearing will mean that the motor torque would also be increased by 4 fold when applied to the load.
This would have been easier if you had stated at the outset that you want to use belts and no other drive means, to accelerate a mass of 25Kgs at a rate of 1G inside a space which will be heated to >120 deg C using nothing but off the shelf components, rather than drip feed small pieces of information whenever a suggestion is made.
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@deckingman Yeah you are right. I'm sorry, I'm a bit under stress and I should have taken more time to pose the actual problem. I sometime forget other people aren't in my head and that it is important to share information. I really appreciate your feedback and I am sorry if I made you lose time.
Yeah, reducing the motor is a good option to increase accuracy of higher pitch belt. I found different 8mm pitch high temperature belts that, I guess, are designed for automotive. I will need larger pulley are they are less supple than smaller pitch, but with reduction on the motor it should be ok.
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@kuon Its possible to get 2GT belt in just about any width. They are made from a huge slab, and spiral cut. If you want to get pricing/details own wider 2GT EPDM, shoot me an email at support at filastruder.
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@elmoret Email away.
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@kuon said in High temperature timing belt:
GT2 12mm wide seems to require custom made pulley
You can find a lot of specialized things like that here: https://www.sdp-si.com/
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@Phaedrux Thanks for the reference. For some reason when searching with google their products do not come out.
