Belt drive and pulley sizes

[j2sip]

Hello,

I'm in the process of designing my 2nd machine which uses belts and pulleys for linear drive. There is an RS-Online Philippines where I conveniently shop but the more I browse the more I get confused about the different widths and sizes. I plan to use 10 tooth 5 mm pitch, 16mm hub width pulleys. One spec sheet that I downloaded suggested using T5 10mm belt. Is that the common practice? Wont the belt "dance" in the extra space in the hub? Will two 1500mm T5 10mm belts be strong enough for an X axis length of 54"?

And lacking actual pictures how does one secure the pulleys to the shaft?

Thanks a lot or your patience.

Jordan

[psiron]

Hi,

The pulleys either have grub screws which tighten down on the shaft OR holes for you to screw into the shaft (drill and tap required).
With regards to the belt widths im sure one of the cnc warlords here will be able to help you with that ;)

[j2sip]

Hello psiron,

Thanks for the quick reply. One question answered. I know they will:)

Jordan

[Robin Hewitt]

I took one look at the RS prices and immediately went for the XL, don't know if yours are similarly priced though :beer:
10t sounds a bit small, only 4 engaged, not a lot of leverage. Being an accuracy freak I'd suggest you pre-tension it way beyond the rating for the motor shaft.

This means a lay shaft with bearings either side of the driving pulley. OTOH once you do that you get a second set of pulleys in the equasion so you can beef up the drivers above 10t and get a nice fat shaft through them.

[8iggles]

I've just had the first run out of mine - 10t 5mm pitch 16mm wide on the X axis and same but 10mm wide on Y axis....I have just got them running through pieces of rubber air hose as a temp direct drive.
For the Z I have used an old G cramp for the acme screw and a sprung 2nd nut to take the backlash up...I'm trying to keep the cost down and so far its working quite well (well nothing beat me so far)
The 10t pulleys are small but it seems to be working ok and next I'm going to reduce by about 4:1 (fingers crossed for fathers day) - I managed to tap out 8mm for 8mm shaft and carry on using the skate bearing theme :)
I have just done a video on youtube if anyone is interested www.youtube.com/user/8iggles#p/a/u/0/FTQ2c-HvNvI Dont expect too much theres still loads to do I just pushed myself to get a run and prove I'm on the right track!
Cheers Shaun

[j2sip]

Thanks for the quick reply guys!


took one look at the RS prices and immediately went for the XL

I may go that route too, just to be sure. Is it the 15mm one? Will it ride ok on the 16mm pulley? I'm kinda worried it might derail during operation. Yes, I'm going to use some kind of tensioning there, and may rig up some belt reduction too.


For the Z I have used an old G cramp for the acme screw and a sprung 2nd nut to take the backlash up

NIce idea. I have some 12" G clamp lying around somewhere. Acme screws are non-existent here.


Thanks again.

Jordan

[8iggles]

The Z axis is an easier one than the X and Y as the force is one way, when the cutter hits the material....so the spring and 2nd nut only have to hold the weight of the spindle.
The ones I have used were the oldest worn sprained things you could imagine...there is sooo much slop in the thread but as long as the slack is held up no worries...I even ran the thread in and out with coarse grinding paste creating even more slop.... :)

[j2sip]

Were the nuts spaced far apart? What are the nuts made of? I could make one out of my wife's chopping board. Are 16mm wide belts useable for 16mm hub width pulley?

[8iggles]

Were the nuts spaced far apart? What are the nuts made of? I could make one out of my wife's chopping board. Are 16mm wide belts useable for 16mm hub width pulley?

The nuts are the are the threaded bit of the of the clamp frame I just cut off most of the frame I didn't want leaving enough to mount to...the second nut is the threaded bit if a second clamp with a tab left on to stop it turning...they are about 1/2" apart but this depends on your spring ( mine was off an old washing machine I think ) I would think you could make one from a chopping board but for me I would have had to get a tap to suit whatever thread I could get and this would cost money!! The square threads work great and even with the sprung nut it is very easy to turn.

The 16mm belt I got, fits ok on the 16mm pulleys and there is a little side clearance...There will be some stretch in the belt but, I only intend to cut foam at first so It will be fine for me

[j2sip]

Thanks a lot. I could use a section of the G clamp rod as a tap. That's what I did with my allthread rod plastic nuts.


The 16mm belt I got, fits ok on the 16mm pulleys and there is a little side clearance...There will be some stretch in the belt but, I only intend to cut foam at first so It will be fine for me

Now that's good news and bad news. I would want to mill and route electric guitar bodies and neck, but i'm expecting a bit of sanding after machining anyway so a little chatter may be Ok. Or I might be wrong.

[8iggles]

2301

Its work in progress but you get the idea

[Robin Hewitt]

Stretch in the belt should not actually affect accuracy, so long as you pre-tension it beyond the expected load.

Just my .02p

[j2sip]

Stretch in the belt should not actually affect accuracy, so long as you pre-tension it beyond the expected load.

That's nice to hear. I was originally planning to use bicycle chains and sprockets but I've read quite a few posts here and at the zone that are against them. Ok, back to the drawing board! Thannks for the replies to my queries. I still have a hundred more.


Jordan

[j2sip]

@8iggles

That's a clever solution you got there. That's what I should do also.

[j2sip]

http://i49.photobucket.com/albums/f251/j2sip/CNC/Likod.jpg
http://i49.photobucket.com/albums/f251/j2sip/CNC/Baba.jpg

Here's a few picture of my design. I just hope it will work.


Jordan

[irving2008]

Nice design - and no reason why it shouldnt work. One criticism if I may; the Z-configuration of the Y-motion belt will be problematic. its inducing a rotational moment on the z-axis which loads the bearings on the high side more than those on the low side. This will wear the bearings unevenly and could result in cantilever stiction. I would redesign that to put in another jockey pulley and make the y-motion belt flat along its length .

[j2sip]

Strange I was thinking of the same thing while driving on the way to the grocery just 3 hours ago. I could arrange the jockey pulley such that the belt's ends will be located lower. That would also eliminate the need of different sizes of gantry uprights! And it would look much better too.

Thanks for the helpful suggestion. I hope you'll find more to correct :)

[j2sip]

http://i49.photobucket.com/albums/f251/j2sip/CNC/newbelt.jpg

Here's the pulley placement redesign as suggested by irving2008. The belt barely cleared the bottom V bearings. It now looked simplier despite the addition of another set of bearing pulley. Thanks a lot for your help.

jordan

[irving2008]

That looks better; the belt tension will pull the tops of the uprights in so depending on the tension and the thickness of the uprights you may need to consider a compression member above or at the belt line. this could simply be a section of tubing, so I'd leave it until you've built it and see if there is measurable deflection.

[John S]

Nice design, one small thing, add a support bearing at the side of the large pulley on the X axis cross shaft to prevent the shaft from whipping and also to keep tension without it bending the shaft.

.

[j2sip]

Thanks guys.

@ irving2008

It will be an all MDF machine. Do you think there will be deflection in that section? its only 200mm x 150mm square rom top to the V bearing line. But I'll put that in mind and incorporate a provision for some kind of reinforcement in that section.

@ John S

There will be support bearings at either sides of the big pulley and another 2 at the ends of the shaft. What I has me worried about is the Y lateral support (where the X motor's located). Do you think it will still provide rigidity as it is now divided into two to make room for the belt tot pass thru?

Again guys thank you very much.


JOrdan

[Robin Hewitt]

Do you think it will still provide rigidity as it is now divided into two to make room for the belt tot pass thru?

Why are you putting it in the middle rather than at one end?

[j2sip]

Why are you putting it in the middle rather than at one end?

Hmmm, another great idea from the good people of the forum! It's worth a try. Actually, it's what I'm gonna do. Why didn't I think of it? it will lessen the umber of support bearing o be use. Ill update my drawings. Thanks again!!!

Jordan