Modifying the drive system of a cross-slide drilling attachment

I wish to upgrade the drive of my cross slide drilling spindle from poly belt to a tooth drive plastic/rubber belt system with of course the associated change in the pulley system. Current drive is from a mains powered non-synchronous motor with a Chinese sourced electronic speed control driving a ¼” capacity drill chuck. Relevant dimensions are: large pulley diameter: 80mm/½”shaft; small pulley dia: 20mm/5/16” shaft; Distance between centres: 85mm; Dia of PU Belt: 5mm. Pulley diameters are approximate. Is anyone able to suggest some commonly available belts sizes and tooth belt pulleys which may be suitable for the job. All suggestions most welcomed.

May I suggest that you look, instead, at Poly-Vee belts and pulleys ?

MichaelG.

Try googling belt/toothedbelt drive calculator, here is the first one I found, it will probably work for you:

**LINK**

You may be lucky enough to find a belt and pulley combination that matches the shaft spacing. If not then an effective belt tensioner can be made using a ball race with a bush loctited in place that has an off centre mounting hole. Bolt this with a suitable spacer off the end plate and adjust the tension by setting the position of the race. I used this arrangement on my mill cross feed, there's a photo on here somewhere.

Edited By John Haine on 02/04/2023 14:22:26

+1 for the suggestion from MichaelG that you go for a narrow Poly-Vee belt rather than toothed. If for no other reason than that the pulleys can easily be made yourself. Just get cunning with a bed stop and spacers to get the Vee spacing right.

Toothed belts can have issues when the centre spacing is short and the difference in pulley sizes large due to the limited wrap angle on the smaller pulley. At your low powers probably mostly noise but you may get premature wear due to the teeth not registering neatly when entering the small pulley. Eye-balling your set up I'd think it to be firmly in what I interpreted from the data as being in the iffy region when I considered a toothed belt set up. Went Poly-Vee using similar wrap angles, moving the motor to set tension, and never regretted it.

John Haine illustrates the textbook set up with a bit more space between the pulleys and a nice ball bearing tensioner to define the belt run.

Toothed belts are excellent devices but there are definitely dragons in the data sheets waiting to chomp the unwary.

Clive

I take the point about using a poly Vee belt rather than the tooth variety especially in terms of being able to make your own pulleys and the ease of setting up. Are there any suggestions as to a possible go-to source offering a range of useful sizes of poly Vee belts.

This is as good a place as any to start looking: **LINK**

https://www.bearingboys.co.uk/Poly-V-Belts-3781-c

… with any luck, I think you could probably re-work your existing pulleys 

MichaelG.

Edited By Michael Gilligan on 02/04/2023 17:42:05

Google 'Belting on line'

Just a note. That motor is a universal type (brush comutated AC/DC) not induction. This is the same as used in traditional hand held electric drills. Good torque and easily controlled with a cheap phase angle (light dimmer) type control.

Robert.

I find this calculator very useful for timing belts as you can play with different pitches, etc. and it "knows" what the prefered tooth counts are.:

https://www.bbman.com/belt-length-calculator/

I'd go for a poly-vee or similar belt for that application though.

I struggled recently to find poly vee belts to suit short centre distances and found Megadyne 'TB2' section belts are available in much shorter lengths: LINK

The design process is all in the technical manual: (PDF)

For example: with an 83.6mm driving pulley, a 20mm driven pulley & a 345mm pitch length belt, you would retain the 85mm centre distance.

The pulleys are fairly straightforward to machine (the profile details are in the PDF above) - you choose the number of ribs depending on the power to be transmitted.

Seem to work OK.

Edited By Andy_G on 02/04/2023 19:22:49