New Build 1000x600x200mm (newbie)

**Clive S** · 08-04-2015

Originally Posted by silyavski

The slots need to be 1mm wider than the OD of the motor mount hole. Some servo motors will not allow that movement because the center part is bigger than nema 23 for example, but i can assure you that even 5 mm possibility to move is ok if you use that calculator. Just tested that theory with my servo motor mounts where it was not possible more play. So on a Nema 23 +-10mm both side from center hole is more than enough. Care should be taken if the mount is milled deep into a plate and the motor needs more play just to pass through and enter at its spot.

The reasoning behind the 30mm is to allow for the possibility to change the pulley ratio if needed. ..Clive

**JAZZCNC** · 08-04-2015

Originally Posted by Clive S

The reasoning behind the 30mm is to allow for the possibility to change the pulley ratio if needed. ..Clive

And excellent reasoning dear Sir. .

**routercnc** · 08-04-2015

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?

**njhussey** · 08-04-2015

The centre hole on a Nema 23 gets awful close......well actually this close:

Click image for larger version.

Name: 20150210_115504.jpg
Views: 398
Size: 215.0 KB
ID: 15115

It's actually thinner on mine now than shown in the picture as I tapped the stepper flanges M5 and machined the slots 5.5mm instead of 4.5mm.....

**Boyan Silyavski** · 09-04-2015

Originally Posted by routercnc

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?

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

**Clive S** · 10-04-2015

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

**JAZZCNC** · 10-04-2015

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.

**njhussey** · 10-04-2015

Originally Posted by Clive S

Neil It is close but it works OK of course you can put washers on the cap heads to spread the load.

I will do Clive, just mounted it at the moment to check it can tension OK and that I'd got the belt length correct before dissassembling for wiring and final re-assembly.

**Jonathan** · 10-04-2015

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:

**Noplace** · 21-04-2015

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!