Minibot Motor Press Fit

I’m trying to press fit “something” to the Tetrix motor with transmission removed. The shaft appears to be 1mm in diameter. What size hole should be drilled / reamed into my part in order to nicely press fit onto the motor shaft?

1.00mm diameter? or something else?

Generally a couple thousandths of an inch interference makes a good press fit. But it depends.

I agree with Jim, .001"-.002" per inch of diameter, so your tolerance is pretty small. What material are you pressing on? The softer it is the more press it can tolerate.

1.0mm? Our motor shafts are 2.5mm in diameter… (0.0984 inches)

We were able to press fit a 3/32 inch (0.0938 inch) hole in a 6061 aluminum rod (.25" OD) onto the shaft without difficulty. Just make sure you support the back of the motor where the shaft “nub” is so you don’t pop out the other side :slight_smile:

Jared is right, it is a 2.5mm shaft. Be careful when you’re press fitting something on there, I can think of other ways to accomplish what you’re trying to ultimately do. Press-fitting may or may not be your best option :cool:

As the others have said…The shafts are 2.5mm. I always try to use a micrometer to measure the exact diameter of each shaft and ensure they are very close to each other. When you are dealing with smaller pieces and press its important to be as accurate as possible.


I used a #41 drill bit which measures .0960 inch. my calipers measured the motor shaft at .0980 in. we are most likely pressing the same “something” onto the motor.

I just got the 1mm number off of a flawed CAD model. Thanks for the clarification.

I can’t - the shaft seems too small to affix a setscrew to. Is it not?

Instead of going with a set screw you could use a “clamp on” style thing you want to attach to the shaft.


I didn’t know clamps came small enough to rigidly fix onto a 2.5mm shaft…

Red loctite can also be used to secure press fits. We have it in a custom gearbox securing a RS775 to a tough box shaft and it has worked great.

Can one use such devices on the minibot?

If you have Loctite 638, then I would recommend that over Red (271) for press fitting something onto a motor.

I was going to mention that, it is actually made for press fitting two smooth objects together, oddly the local autoparts stores here didn’t sell it even though it is often used for bearings in cars. So we settled for red loctite which works in low torque situations (like our lifter)

But similarly, I am not sure 638 is technically allowed on the minibot where-as Loctite designed for thread-locking is.

I would like to introduce you to a wonderful site of utilities for the shop:

Many, many programs that calculate whatever you need to do in the shop. Your answer should be found with the FITS program.

Go up one level and you will find a bunch of math programs as well.

I have also noticed that the KOP CAD models from PTC have incorrect diameters on the motor shafts.

McMaster has set screw collars that are as small as 2mm bore…

Those are not exactly what i was talking about though. I was thinking about something like a 2 piece clamp on shaft collar. Lets hypothetically say you were trying to attach a wheel onto the shaft, you could make the wheel 2 pieces and put it together like a 2 piece shaft collar.

Set screw collar with 2mm bore: PN: 57485K61
The OD on this one is 6.4mm that seems like plenty for you to ream it out to 2.5mm ID if you wanted to

2 piece shaft collars:


Are these legal minibot materials? Do they fall under “S. Mechanical fasteners”?

We found that in aluminum a sharp 3/32" bit at the right feed rate produces a hole that is a nice press fit on the tetrix motor.

I would argue that the are indeed mechanical fasteners. However you could always just make them out of aluminium. McMaster provides drawings for their parts and sometimes even CAD which makes replicating them, whether it is to use a different material or to save some money, quite easy.

If you made them out of aluminium you could be totally sure that they were legal and you could modify the design a bit to mesh easily with the system you already want to work with. The nice thing about the “clamp on” is that you don’t have to be as precise with your machining, press fits can be tricky, but with a clamp on collar you can be off by quite a bit more and make up for it by tightening the bolt a bit more.

You could easily adapt the idea of a clamp on collar to make a clamp on wheel…