View Full Version : Spoke to some timing belt companies, intersting stuff........

15-06-2010, 04:07 PM
Hey everyone,

Anyone who have seen some of my other threads may remember that I am trying to source materials in the UK to make a machine similar to the one found on the automatedwoodworks.com website. As most things are in imperial sizes I am trying to source the metric equivalent.

One thing I am dubious about is the timing ‘L’ and ‘XL’ type belt setup. There are other alternatives such as chain however I am satisfied that “I” will be happy with the performance of the belt operation. I only cut basic stuff out so I think it will suffice.

I am writing this thread as I spoke to 2 belt companies in the UK today, the most helpful being Cross + Morse. I like so many others have concerns over the belts either stretching or shrinking or even wearing quickly. I explained the application to one of the engineers who assured me that if setup correctly the belts would perform exceptionally well in this application. I specifically asked about stretching to which he started to explain the advancements that have been made to eliminate these problems. He did say that stretching could occur in certain applications however this is so small that you would not notice it due to the teeth and pulley arrangement.

I also asked about belt tensioning as I have little experience in this. I have used ‘V’ belts on other equipment for years and these were always as tight as guitar strings. He explained that the tension on each belt does not need to be high and said that the length on the belt (not circumference, this is from centre pulley to centre pulley) should be divided by 64, this will give the result of the allowed ‘slack’. E.g. for a 1000mm measurement (pulley to pulley) there should be around 16mm movement in the belt when you move it with fingers. Not sure about you but I found this interesting as I was getting ready to tighten the hell out of it with a tensioning arm!

He explained that by not having the tension ramped up allows the teeth on the belt to actively sync with the pulley. In this instance any unforeseen changes in the belt shape (this includes any general force on the belt) will not result in any degrade in performance. Apparently the meshing of the teeth and pulley in these systems is extremely accurate.
If anyone is looking for timing belt information, Cross + Morse were extremely helpful. Their website is at http://www.cross-morse.co.uk/timing_belt.asp (http://www.cross-morse.co.uk/timing_belt.asp)

I am definitely convinced more now that I have spoken to them. I hope this information helps anyone looking for timing belt information anyway.

I just need to solve the ratio and reduction stuff now and I will feel much better. I feel another post coming on.................... :tongue:

15-06-2010, 05:29 PM
I wouldnt get too hung up on the ratio issue. UNless you're on the margins just near enough is good enough. By way of example, a 20tooth pulley on a 5mm pitch (http://uk.farnell.com/synchroflex/ls27t5-20-2/pulley-timing-16mmx20teeth/dp/7092519)belt has a circumference of 100mm (20 x 5) and a radius of 15mm.

Assuming your gantry weighs in at 20kg you need around 5g acceleration for accurate path following, so the force you need is 20 * 5 = 100N (which suggests you could get away with a 10mm wide belt, max 350N per 10mm width) Your motor is driving the belt at a radius of 15mm so the torque required is 100N@ 0.015m = 1.5Nm - now this isnt the static torque of the motor, its the torque required at full speed. If you have a 1.5Nm holding torque motor, you need to gear it down by say 1:3. Driving the belt pulley with a 45tooth needs a 15tooth on the motor. Assuming a maximum of 300rpm on the motor gives a maximum of 100rpm at the belt = 100 * 100mm/min or 10m/min for rapids (on full step) and a maximum resolution of 100mm/(200 * 3) = .167mm (on fullstep)

Of course you can go to lower gearing with lower acceleration as long as your cutting speeds are lower as well. You'll need to work this through for your own. The tricky bit from a construction perspective is the driving of the 20tooth belt pulley from the 45tooth one as the 45tooth is larger (and would probably be outboard of the belt to avoid having a slot in the bed.

15-06-2010, 06:47 PM
I think I'm in a bit of trouble here, I don't understand any of that :-|

I have kind of copied the original design including the number of teeth used on each pulley. The designer uses a 70t reduction pulley which I hadto change to 72t, other than that I have sourced exactly the same pulley and shaft sizes.

I'd like to use r&p if I was being honest with myself but it all seems to be very expensive which is a shame.

Thanks very much for your excellent response, hopefully if I stare at it long enough i might understand it lol

15-06-2010, 08:21 PM
Sadly the designer Steve Marsh has been very economical with any details of his pulley/belt arrangement on his website... I can't find any decent pics....

maybe if you explained the drive setup I could explain it to you...

15-06-2010, 08:44 PM
Sure that would be great, I'll PM what I have.

Thanks very much.

15-06-2010, 10:21 PM
PM replied to... 72T will be fine...

16-06-2010, 12:09 AM
he using 72/70... 24/25 and 15/16...I spent a lot of time studying the pics and determining his sizes. I too am using his principals in my build. As for the belt i am using 15mm HTD. This is more than man enough as am not expecting to be cutting metals at 50mph :-)

16-06-2010, 12:36 AM
The L belt is 9.525mm (3/8"), nasty non-metric size. I'd prefer 5mm or 10mm. What pulley are you using on 15mm pitch belt?

16-06-2010, 10:12 AM
I hate imerial sizes too, my problem is I have been give the pulley sizes and belt sizes and kind of followed that. If I knew what I was doing I would have changed them. This is mainly becuase I will offer a full BOM to everyone once I have completed the project and it would be nice for all parts to be commonly sourced in the UK.

I have sourced everything so far except the drives, belts & pulleys. I was going to buy the Gecko 540 kit only becuase it all plugs in which saves me alot of worry. I am pretty handy with fabrication but not too good with electrics unless the plans are fool proof (and I mean fool proof).

I dont expect the build to be brilliant but if all parts could be sourced in the UK it reduces shipping costs from other countries for anyone else wanting to jump in and build someting similar, currently the only option I have found is the 8x4 blackfoot which is very pricey.

I bloody hate imperial sizes, what a waste of time......

16-06-2010, 01:34 PM
Its 5mm pitch and 15mm wide

16-06-2010, 01:34 PM
HTD5 pulley's and belt

16-06-2010, 01:38 PM
Try ERIKS where i got mine from. It is an expensive outlay but comparible to screws, I will try and update my build log soon. Don't buy the rubber belt a complete false a oconomy, Time gets less and less everyday, i have to finish putting my southbend back together to make room to finish it off (tiny garage)

16-06-2010, 02:46 PM
Have a look here http://www.technobots.co.uk/acatalog/Shop_Front_Pulleys___Cams_404.html for your pulleys and belts, this is where u got mine from, if you cant see what your after give them a ring, thats what i did. They are very helpfull!

16-06-2010, 03:45 PM
Thanks, ill take a look

16-06-2010, 10:37 PM
technobot do not do the sizes or open ended belt but they are very helpful

23-09-2010, 03:51 AM
Have a look here http://www.technobots.co.uk/acatalog/Shop_Front_Pulleys___Cams_404.html for your pulleys and belts, this is where u got mine from,

+1 on helpful!
AdCNC - Now that your machine has been running a while ... i appreciate its servos not steppers ... but any comments / after thoughts on belt size/pitch/width/type, gear size/material, ratios or the design you used to allow for tension adjust?

If you remember .. what were the specs of the belt + pulleys you used?

*looking 90% like it will be SY60 steppers (48v BiPol Parrell) for 2x Xaxis ballscrews 1100mm long each hauling 35kg of Y + Z + router