I think what silyavski is saying is that the centre hole on a nema 23 needs to be about 40mm dia to clear the 38mm raised boss on the end of the motor. If you cut long slots for the motor mounting then as these are about 47mm apart and about 6mm across then they get very close/ too close to the centre hole. On a servo motor this overlap sound like it is worse (don't own servos myself)
If you need a long adjustment slot (more than +- 10mm) a workaround could be to lightly pocket the 40mm centre clearance instead of a complete cut out ? Away from computer so can't check this for sure. Is there another way?
Last edited by njhussey; 08-04-2015 at 02:07 PM.Neil...
Exactly thats what i meant. Thanks!
There must be many ways to do a thing but here is how i think:
-more or less center to center around 90mm, so that usually the belt is in the region of 270 to 315mm depending on the ratio.
-Dont have the time now to play and prove it but at that distance/look at the Nema 23 mount/ was possible to lower the small pulley teeth count and rise the other , so as i remember 1:1 to 1:2 was possible may be even more, without changing anything. I just remember that when doing the yellow machine there was that consideration also.
Same with the servo machine now i am building but not to such extend, due to shorter play possibility.
Below you will see a picture with the maximum movement according to me and having in mind the parts were laser cut from steel. So maybe from aluminum could be more play.
Nothing to prove with all that , just sharing for your consideration and if possible to help avoiding errors. Thanks
PS. The measures are radiuses, possible play and size of the thinnest part there
Last edited by Boyan Silyavski; 09-04-2015 at 09:38 PM.
Neil It is close but it works OK of course you can put washers on the cap heads to spread the load.
Silyavski Another way would be to mount the motor on to a plate with no adjustments and then mount that plate with slots on top of another plate so that the motor and its plate would be adjustable. ..Clive
Nema 23 Boss is 38mm-/+0.1 the whole point of the boss is to have close fit to stop movement so making 40mm hole is wrong way to go aout it. 38.3mm usually is just enough for nice snug fit. When done this way then there's no problem with slots or mounting holes if again they are milled to correct size also.!
IF you don't have room for slot adjustment then use an idler gear to take tension up. Not ideal way to do it but will get the job done.
The Nema 23 boss is 1.5" - so 38.1mm. It's there to allow the motor to be mounted concentrically to another shaft by machining the mount to be a close fit on the 38.1mm diameter. In the case here, there is nothing to align concentric to, so all that is required is a cutout of enough to allow the boss to fit. There's often a +-0.05mm tolerance on the boss diameter, so in the past I've machined the cutouts to 38.2mm to be on the safe side. You don't want it tight else it will be harder to tension the belt. Also the cutout for the boss needn't go all the way through the material - 2mm deep would be plenty. e.g:
thanks guys for all the info, one question on another topic: how do you mount the linear rails on steel boxes/frames ?
I'm thinking of designing the body out of that since its readily available locally instead of alu t-slot extrusions but I don't know the technique you use to mount them, seems you cant access under to put nuts for the bolts!
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