High speed belts?

[jmkasunich]

I have an 18000 RPM 400W (approx 1/2 HP) induction motor and a matching VFD. I want to build a small (1/8" diameter tools) spindle, with a top speed of 30,000 to 36,000 RPM - about a 1.6:1 or 2:1 speed ratio.

I've done a lot of googling and reading over the last few weeks/months, trying to determine the best belt option.

The driven (spindle) pulley will be between 3/4" and 1" in diameter. The driving (motor) pulley will be between 1.25" and 2" in diameter. A 1.25" motor pulley will give a maximum belt speed of just under 6000 FPM, the 2" pulley would take the belt speed up to 9400 FPM. Torque at the motor is 1.75 lb-inch (or 0.2 N-m for the metric folks). Torque at the spindle will be roughly 1 lb-in, depending on the actual reduction ratio.

I initially considered timing belts. A table at this site: http://www.roymech.co.uk/Useful_Tabl...ing_belts.html
says that a 1/4" wide MXL belt can handle 0.2 N-m for pulley sizes of 3/4" or more. However, this chart (same site): http://www.roymech.co.uk/images11/timing_belt_3.gif
says that MXL tops out at 20K RPM.

There are other belt profiles - HTD and GT for example. However, I haven't found anything that is specified for this speed. I've got a long Gates document on my other computer - can't refer to it right now, but I've been through it twice with no luck. All the charts top out at 10K RPM or so.

The other options that I've seen used for high speed modest power drives are round (o-ring) style belts, and flat belts. But finding technical info has been very difficult - hence this posting.

O-ring belts are somewhat attractive since they are narrow - I could probably make a pair of step pulleys and have two speed ranges. But they are thicker, which means more flexing and heating as they go around small pulleys at high speed. Many of the belts I've looked at have minimum pulley sizes of 1.5" or more. McMaster does have 3/32" diameter belts that are listed as usable on 3/4" pulleys, but that size seems very small for this power level - and I can't find any data to confirm or deny that. None of the belts I've looked at listed maximum speeds. I'm gonna keep looking, but my gut says round belts won't work.

That leaves flat belts. Page 1032 at McMaster Carr shows both urethane and nitrile-coated nylon belts with minimum pulley sizes of 5/8" or less. Widths range from 3/16" to 1/2". No maximum speed information listed there, but other sources seem to indicate that flat belts in general are good at 6000 to 10000 FPM, which covers my range.

What I haven't been able to find is how to calculate the width and belt tension that I will need. I've found formulas on a few websites, but they are always for leather belts in much larger sizes.

Many of the websites that I've run across are for urethane belts used as conveyors, rather than as power transmission.

Does anyone here have any experience with small, fast belt drive designs? Any suggestions?

Thanks,

[RICHARD ZASTROW]

This company may be able to help. www.wmsopko.com/flatbelts-a.htm

Dick Z

[emcnut]

round belts have been around (no pun intended) a long time for a reason
They are simple,reliable and take a lot of punishment
I would bite the bullet,make your pullies 50% bigger than you intended
Buy a 1/4" nitrile o-ring of suitable size and give it a go
Dont get me wrong I don't dislike toothed belts, but in some cases they dont hack it

[harryn]

A possible resource for your search.

http://www.brecoflex.com/

[Mike Everman]

Have you considered a simple gear pass?
A set of 96 pitch gears would be smooth and fast.

[JLSD]

Hi,
"If it were me" I'd look hard at "Poly V" belts.
Common in washers, tumble driers, modern aux. drives on cars.
Come in several pitches, from memory 1/16", 1/11", 1/7" and bigger.
Most applications lnclude a pretty small pulley and big ratio, so they'll stand a tight bend.
In a previous life I built some test rigs for the manufacturer, a typical washing machine belt gets proved shifting 4 H.P. using one minimum dia. pulley, a back-bend pulley, and about 100kg. tension!! Expectation was belt failure at about 1000 hrs.
For what you want, any section would eat it.
If this looks like overkill, a "cheap and cheerful" way to go would be vac. beater belts. I've seen a few "O-ring" style drives, and the right flat "rubber band" beats all.
Hope this helps, regards,
John.

[jmkasunich]

Well, Dick Z pointed me in the right direction, but that was only the start of a long and winding road.

Sopko sells flat belts, but they don't have any technical info. They pointed me to their supplier, Jason Industrial. The folks at Jason's main office also couldn't help, but they pointed me to their engineer.

Fortunately I was making my calls on the morning of Good Friday.... Dave the engineer was bored since nobody was calling him, and I got at about 45 minutes of his wisdom.

One of the posters in this thread mentioned multi-rib V-belts. Dave said that they could work, but the readily available "J" series is too big. The calculated width of a "J" series belt to handle my application is 1 rib. The narrowest belts I could find are 4 ribs wide. In addition, the "J" series wouldn't really like going around my small pulley.

There is an "H" series multi-rib that is smaller - a 4-rib or so "H" belt would work well, but "H" belts are very uncommon and would be special order items. That would be OK if I was an OEM making hundreds of spindles, not so good for a one-off.

We also talked about flat belts. Flat belts are very flexible, and don't mind going around small pulleys. They also work well at high speeds - belts speeds from 6500 to 9000 feet-per-minute are fine. (My application works out to about 5000 feet-per-minute.) We calculated that a belt about 3/16" wide would be enough to handle my power if tensioned properly. The hitch is that a belt that narrow might not track properly.

Dave asked me why I wasn't using timing belts, and I said that I couldn't find any specs that support speeds over 10,000 or so RPM. Both Gates and Jason have design documents that top out around there. But he said that the catalogs are very conservative when rating speed, especially since I'm not going to be running 24 hours a day. As long as my surface speed isn't much over 6500 fpm, a MXL timing belt will work fine.

I did the math and came up with a minimum width of a little under 3/16" given my power level and operating conditions. McMaster has MXL belts in 1/8", 3/16", and 1/4", but they only have pulleys in 1/8" and 1/4". So I decided to be conservative. I am using a 1/4" wide MXL timing belt on 1/4" wide pulleys. I'm using a 30 tooth pulley on the spindle, and haven't decided between 42 and 48 teeth on the motor (for top speeds of 25,200 and 28,800 RPM respectively).

Thanks everyone for your suggestions and input.

John

[harryn]

So - with all of that great help from engineer Dave, I hope you are planning to buy from his company. Good professional advice is well worth a few bucks.

[jmkasunich]

I hope you are planning to buy from his company

I'd like to - but they don't sell retail. They simply can't make money on small orders (my belt will cost about $5 - they would probably spend more than that processing the invoice.)

I'll buy from McMaster or someone else who does sell retail. I'll certainly remember the company, and if I ever find myself in a situation where I need a bunch of belts, they'll be at the top of my list.

I made it clear to Dave at the very beginning of the call that I was doing a hobby project, and would have understood if he couldn't help me. Initially all I was asking for was links to technical info, catalogs, etc. But he said he was "twiddling his thumbs" that day (nothing to do). He seemed to enjoy our conversation as much as I did. He said he doesn't get to do high speed designs very often.

[rowbare]

Would a belt from a Taig mill work? It is a 3mm PolyV. On a Taig it is used with a 1/4 hp motor at 10,000 rpm. The torque transmitted by your 1/2 HP at higher speed should be similar.

You can get the belt and a pair of stepped pulleys here: http://www.positiveflow.com/taigacc.htm or from any Taig dealer (this page has pics).