[Gorillakilla]

There doesn't seem to be that much information about this. My main questions concerned the classification of them, such as H, MXL, XL, etc... I dont need exact numbers, but if my steppers are 269 oz-in, which type should I be looking into? Also, if anyone knows where to find belt and pulley calculations that would be appreciated.

[NC Cams]

The designations you mention are belt series that specify belt pitch.profile and torque capability.

Get hold of the Stock Drive Products catalog, they can provide you with timing belt drive calculation help. Belt width and pitch will determine how much power you can drive/handle.

Look up timing belt drives by Gates or Uniroyal on Google.

[ger21]

The catalogs mentioned by NC Cams are at www.sdp-si.com

GT2 profile belts are stonger and have less backlash than most others.

[planescott]

This is the gt2 series 15mm wide I am using on my machine they also have a 9mm wide which you might be interested in.

[IMG]IM000810.JPG[/IMG] :stickpoke

[Apples]

I am using the GT2 15mm ones on my cnc plasma table. The gantry on this weights around 50kg, 100lbs.

Peter
Australia

[planescott]

I seen the video of your machine apples, very cool!!!

[Gorillakilla]

I was looking through the World of Timing Belts on SDP/SI's website, and ran across a rated horsepower vs rpm graph (page 4). Does the graph indicate that the higher the rpms, the more horsepower a belt can take? That seems counter intuitive.

[Geof]

I was looking through the World of Timing Belts on SDP/SI's website, and ran across a rated horsepower vs rpm graph (page 4). Does the graph indicate that the higher the rpms, the more horsepower a belt can take? That seems counter intuitive.

No. not really. There are two primary limits to a belt's capacity; any belt or a chain drive for that matter. One limit is how much tension can be put on the belt the other is how fast it can run. Belt tension equates to torque on the pulleys and power is torque x rpm so for a given tension the power transmitted goes up with the belt speed.

[NC Cams]

In the form of an equation:

HP = TxRPM/5252

where HP = Horsepower
T = torque in ft-lb (multipy by 12 to change to in-lb and again by 16 to conver to in-oz)
RPM = speed in RPM
5252 is necessary conversion factor.

Thus, for a CONSTANT hp, as torque increases, RPM must decrease and vice versa.

Unless you have a torque/rpm curve for a motor, any assumptions made re: torque vs RPM relationships are purely SWAG's and are not necesssarily valid.

Torque (with respect to belts) affects the number of strands in tension (a function of width). The number of teeth in contact with the belt affects tooth load. The pitch diameter of the pulley (IE: strand tension times pitch radius) affects the torque the belt can transmitted.

The equations in the handbooks usually take you thru the math and also provide you with appropriate shock load factors that MUST also be considered.

[keitht]

hi all
I am considering converting my larger mill to CNC because I just can't manage the bigge jobs on the Taig.
Anyway I today went to my local bearing supplier and he said that I should be using anti-backlash timing pulleys and not standard ones.
Is this correct ?
Regards
Keith

[WayneHill]

Keitht:

Yes. Look at the GT2 style timing belts ger21 (Gerry) mentioned above.

[ViperTX]

That is correct.

[NC Cams]

I have older HTD's on 3 cnc lathes and a cnc mill - 8 axes total. The lathes haven't be runoff lately but the mill easily holds sizing of masters to within 0.0001".

I'd give you a qualified "it doesn't matter if the belts are sized and tensioned correctly as ours are" replly.

Naturally, you'd want the latest technology but realistically, you may not need it - we get by just fine with HTD sprockets on our factory built Bridgeport EZTRAK mill. No intent to update for the sake of updating as we're doing just fine with "legacy" (perhaps orphan) technology.

[WhiteTiger]

http://www.autos.co.kr/BELT/Timing_B...ng_belts_.html

An old site but a good one for the basics of timing belts. Used their dimensions to grind the fly cutter I machined my L series pulleys with, work just fine.



Tiger

[pminmo]

If a person was looking to couple a timing belt to a 200ozin stepper to a shaft say a 2 to 1 ratio. Low cost, what would you recommend? or what should a person look for?

[NC Cams]

I don't feel that you can do much price shopping when it comes to timing belts.'

Why? Availability. You have to find the pitch length you need once you determine the belt config and width needed to carry your load.

Since the market is "mature", you aren't going to see much price chopping.

They got it, you want it, you'll ultimately pay for it. Trick is to shop til you drop and hope to find a fair price....

[jguillen08]

My machine has 150 oz-in servo motors. I am using a 3:1 ratio,the belts are XL series and they seem to be doing just fine.

[pminmo]

I wish somebody would put together a "tutorial" on timing belts for DIY cnc. Manufactureres, pro's and cons, costs, performance............

[energyforce]

What about a belt that has a span (head pulley to tail pulley) of 11feet, with a tensioner at the tail? Im not worried about belt strength, but more about losing precision. Im concerned that there would be a considerable amount of sag, and that this sag would impact the accuracy, and if it will how much? What about belt deflection? If the belt will deflect for instance 1mm per foot at max torgue, that means it could deflect 1cm in a 10 foot span?

The bottom of the belt will be attached to the gantry to move it, and the top will be free (could install some idlers). Input? I have attached a pic.

[ger21]

Why not fix the belt at the ends, and put the motor on the gantry, with two idlers to wrap the belt around the "pinion" pulley. This cuts your belt length in half, and should cut your stretch, or sag, in half.

Or, go to a bigger belt that you can put more tension on it.