Parts Problems

Seems like nearly everything I ordered from Mcmaster-Carr is slightly off.

The 8mm rod (88625K67) was 3' instead of 1m, which meant I had to buy about twice as many. Local hardware store had something that was close enough, so that wasn't too bad.

The springs (9657K108) don't fit over the studding. I'll have to find a replacement.

The toothed belts (1679K683) and pulleys (1375K39, 1375K57) don't match the pitch of the RP'd pulleys. Not sure if they're close enough or if they're scrap. I can probably get away with using one pulley and belt for the X axis but I'm not sure about the Y and Z.

Has anyone used the McMaster belts with the RP'd pulleys yet?

The McMaster belt is 0.08" = 2.032mm pitch the pulleys are 2.5mm pitch I would expect that to give a problem we can supply belt or it's using the McMaster pulleys and modifying the drive connectors for the Z axis simply mount the McMaster pulley above the coupling/pulley for the Y axis you will need to cut back the motor shaft and cut the coupling down and drill a new grub screw hole.

Also the Diagonal ties do not have a grub screw as we found if you tighten the 2 nuts quite tight they will stop the diagonal tie rod from coming off.

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Ian
[www.bitsfrombytes.com]

Ah, OK, I think I've got it. In order to use the McMaster belts and pulleys, I need to:

1. Drill out the hubs to 5/16" (or 8mm).
2. Work out a way to couple the Y and Z motors.

I'm leaning toward buying/making aluminum couplings. Both look like they'll be taking a lot of shear and torque stress. Closest I could find off-the-shelf was Mcmaster's part 2424K11. It's a 1/4" set screw coupling but it's only 1/2" OD, which doesn't leave much room for boring out to 5/16". Still, at $6 a piece, it might be worth picking up a couple to try out. I'm planning on ruining at least one pulley by boring them out, so I might as well order the couplings while I'm at it. :-)



//Also the Diagonal ties do not have a grub screw as we found if you tighten the 2 nuts quite tight they will stop the diagonal tie rod from coming off//

I see what you mean. Thanks, I was wondering how that was supposed to work. I just tried it with a couple pieces of scrap and was able to tighten it to where it doesn't slip. Works better with the 8mm rod. The 5/16" will probably need a shim.

McMaster also sells a neat motor coupling that comes in parts so you can select two separate diameters. They're called spider shaft, or something like that. It looks like it's going to work fine for my Z and Y axes.

Kyle

Spider couplings are nice.

//McMaster also sells a neat motor coupling that comes in parts so you can select two separate diameters//

I saw those (or maybe it was an Oldham coupling) and wasn't sure if that would work, given the shearing force from the belt. I'd probably go with something like that if there were a support and bearing on the non-motor side of the coupling. I'm tempted to rig up some sort of support on either side of the coupling to take the load off it and the stepper motor.


Yesterday, I went wandering around Home Depot with various bits from the Darwin kit, to see what I could use.

For the motor couplings, I ended up using a threaded rod coupling, bored out to the appropriate diameters and held in place with a couple grub screws.

I also found some compression springs that seem like they'll work for the anti-backlash assembly. They were over with the screen door accessories.

I just went and looked at the McMaster site again. I got it wrong. The spider couplings are completely different from the Oldham couplings. It was the Oldhams that looked they would have a problem with shearing.

degroof Wrote:
-------------------------------------------------------
>
> For the motor couplings, I ended up using a
> threaded rod coupling, bored out to the
> appropriate diameters and held in place with a
> couple grub screws.

Here's a picture of one of these couplings in place.



Edited 1 time(s). Last edit at 03/07/2008 10:01AM by Steve DeGroof.