Ha ha I think I will leave American politics to Americans so no comment from me regards that

I have a DA pencil chuck so if I go down that route it is what I will use but thanks all he same.

Hood

Hood,

It's going to be an interesting project with the cooling channels

I would still replace the timing belt with a V-belt or O-ring. Timing belts are just not designed for such high speeds. What matters for a belt is not the RPM, but rather the linear speed it runs at. A 20mm diameter timing pulley carrying a belt and revolving at 3000RPM would probably have no issues, but a 100mm pulley rotating at the same speed would mean a much higher linear speed of the belt and wouldn't be OK.

I have a grinder which I built few years ago and it uses O-Rings for driving the shafts. Have never had an issue with them, and they transfer quite a moment compared to the spindle speeded you built. The pulleys have a round profile to match the O-ring. Was pretty easy to make them. I ground a HSS tool bit to the appropriate radius.

Dan

Daniel
 The driver pulley I am using is about 45mm OD and will be spinning at about 3000 to 3800rpm, the driven pulley is approx 12mm OD so will be going 3.75 times faster.
'O' ring or vee may be the way to go but as drilling cooling holes will probably be done whichever way I go I will try it first with the timing belt.
Hood

Hood,

Oh... so speed is not really an issue I would say. You could get by with the timing belt and the cooling. Another thing is that if you wanted a quieter and smoother operation, then an O-ring would be beneficial. Unless you've already made your decision about drilling cooling holes in whatever case or you have other reasons for it than the heat generated by the belt, I am pretty confident that an O-ring configuration wouldn't need them.

Daniel

not quite sure what you are meaning by a collet extender?

Same thing Simpson is talking about.
Good to hear about the link belting, as I'm planning on using some of it.

Daniel
 holes bored will be the quickest and easiest, if it doesnt work then I will look at vee or 'O' ring.
On that subject, how tight do you need the 'O' ring, does it need stretched a bit or just enough to not have  any slop?

Sam
 Ok thanks and yes the belts are good in boats where the bilges are full of salt water, diesel oil and all sorts of other nasties so should be fine almost any other place

Hood

"Timing belts are just not designed for such high speeds"   This statement is inaccurate. For those who prefer observation over engineering specs, note the black thing on the front a blown top fuel dragster engine  . . . 10,000 RPM 6" dia pulley . . do the math . . . or the primary drive of a custom Chopper (motorcycle), or the dry sump oil pump on indy cars or perhaps just the cam drive on many modern automobile engines. In machine tools, some surface grinders have 'timing belt' drives on the grinding wheels.

And . . .  all of these real world examples use the OLD trapezoid tooth profile. The newer curvilinear profiles are far better. Flat belts have been used for years for high speed applications like tool post grinders and so on because they are less prone to whipping like V belts which have a much larger tangential cross section. A 'timing belt' is similar to a flat belt in dynamics, except that there is no slippage, which coincidentally is actually where the heat comes from in v-belts, round belts and flat belts.

Round belts come in two types; elastic and corded. Example of elastic are vacuum cleaner belts. Belts with chords don't stretch (much) and you must follow the manuf specs for the type of belt . . specifically the type of chord.

In any case, no matter what belt drive setup is chosen, the amount of heat contributed by the belt is minuscule. The heat comes from the bearings.

Hood,

Yes, extra cooling sure wouldn't hurt in any case. Especially if it's so easy to do

An O-ring is stretchable by nature and I don't know of any 'scientific' recommendations for its tension. And here is its advantage, I think, you don't need any tensioning mechanism. I designed my drives so that the O-ring is a bit stretched - about 5mm shorter than required (if memory serves me well) worked fine for me. But it would depend on the overall length of the belt. Mine were made from long stock O-ring, cut to size and melt joined the ends.

Steve,

Correction: V-belts work better at high speeds. Much better in most cases! Timing belts produce noise (and heat) as the speed increases - this is a fact! As the speed increases you have to consider for precise aligning of the timing belt. As the speed increases the teeth wear becomes more of an issue. For high speed application not requiring positive belt grip don't use timing belts. There are big industrial lathes with spindle speeds to 18,000RPM capable of rigid tapping which use poly V belts - NOT timing belts.

Daniel

Thanks for the info Daniel, will see how the cooling goes and decide from there, may even make a wee gearbox up as I found some nice gears from an old encoder drive thing
Cooling holes have been drilled and seem to be fine, just have to dismantle and rebuild with the shafts/pulleys/belt in place and test it out, only problem is I need to replace the driveshafts in the van today so wont get a chance to test it out.

Hood

"Wee Gearbox"... hmm... sounds good, but what is it anyway

Daniel