I need help choosing a belt design for 10K RPM Spindle with Treadmill motor

[EricMack]

I love Acorn CNC. I have so much to learn but this forum and the documentation have been very helpful. After setting up a Sherline Mill on Centroid Acorn. I'm now retrofitting a Folken Mill with Centroid Acorn. I have the motors and mounting brackets as well as control box coming along nicely.

Now, I need help choosing appropriate belts and pulleys to drive my spindle at 10K RPM.

The Folken mill came very expensive high-precision 45,000 RPM NSK Spindles and matching motor (which require very expensive controllers that I do not have) so I am planning to sell the NSK Spindles. In place, I intend to purchase A Sherline Cartridge Spindle calibrated for 10K RPM. To drive this, I will use a [claimed] 1.5HP treadmill motor which is more powerful than the 1 /2-2/3 HP motor on my Sherline.

My primary reason for choosing the Sherline 2.5" Spindle Cartridge https://www.sherline.com/product/6509-2 ... lt-pulley/ is that it is low-cost ($135 with no Pulley), easily mounted on the Folken mill, and I already have a lot of tooling and end mill holders for this size spindle. So, it will lower my start-up cost for now until I learn enough to justify something else.

On to the selection of belts and pulleys for high speed 10K RPM Operation.

Before posting my question, I did my homework.

One option is to purchase the 10K RPM pulley set from Sherline which uses the same small reinforced urethane V-drive belt (MB330) from their normal spindle motor intended for 2800 RPM. Another option is to choose some kind of timing belt and pulley. My concern is that it uses the same drive belt as their standard system designed to run at 2800 RPM. I wonder if that is a good choice with a motor that is 2-3 x more powerful.

Another option is some kind of timing belt and pulleys. Not knowing the pros and cons of V-belt vs timing belt, I did some research and here is what I understand: I learned that a v-groove belt or similar is much quieter than a timing belt with teeth, but it puts a side load on the spindle. A timing belt (e.g. XL, MXL 3/8” width) applies little side-load, but it can apparently be very noisy at high speeds as each groove traps air. (No idea how noisy, I'm just sharing what I am read.)

So, has anyone been down this path before or have knowledge to offer advice and recommendations for a style of pulley and belt that I should consider?

Thanks,
Eric

Update: I have attached a drawing with some details. I also attached a photo of the Treadmill motor and its multi-groove flywheel.

[Richards]

There's a little math required to determine the ratio required. What is the maximum speed of the motor? That maximum speed determines the ratio. For instance, if the motor can spin up to 2,000 RPM and you need 10,000 RPM, you divide 10,000 by 2,000 to get 5:1 ratio. Then you would put a pulley that has 5X as many teeth on the motor as the pulley on the spindle, i.e., 50 tooth pulley on the motor and 10 tooth pulley on the spindle. If the motor can spin at 5,000 (like a DMM DYN2 750 motor with 240VAC), then you would only need a 2:1 ratio, with a pulley on the motor that has 2X as many teeth as the motor on the spindle.

I've used XL size pulleys and belts on other applications, but I have never used XL pulleys at the speeds that you need. I have not used the smaller MXL pulleys which might be a better choice. The XL has a 0.2" pitch and the MXL pulley has a 0.08" pitch. The MXL pulleys are much smaller meaning less mass. At 10,000 RPM, it seems to me that less mass would be prefered.

[tblough]

For a spindle, you should look at poly-v belts (serpentine belts on your car). They are much quieter than cogged belts. Here you go: http://www.powerparts.it/contitech_pdf/ ... ltirib.pdf - chapter 3 is where the belt design begins.

[EricMack]

There's a little math required to determine the ratio required. ...

Richards, thank you for your response.

I should have been more clear that the help I was looking for for to determine optimum belt style and design for these speeds. I have updated the title of my post. Thanks.

I have a wonderful belt calculator for determining ratios and lengths of belts, etc.

But since you asked... the Sherline spindle cartridge is rated for a maximum of 10K RPM. The motor I have has a maximum speed of 4800, so my plan is to use a 2:1 ratio to result in 9600 RPM. I know that this would mean less torque to the spindle but for the small stuff I want to do and the fact that I'm using a motor that is 2-3 x the power of my current Sherline motor, I think it will be a big improvement.

[EricMack]

For a spindle, you should look at poly-v belts (serpentine belts on your car). They are much quieter than cogged timing belts. Here you go: http://www.powerparts.it/contitech_pdf/ ... ltirib.pdf - chapter 3 is where the belt design begins.

Tom, thank you. I will study the PDF. That is the kind of info I was looking for. In scouring the Internet I have even seen some people cut off the poly-v part of the flywheel to turn it into a pulley. It does make sense that a poly-v (serpentine) style of belt would be less noisy than a cogged timing belt due to less trapped air in the teeth. I guess I'll need to read up to see if those belts are appropriate at 10K RPM.

Thank you for the tip and link...

Eric

UPDATE:

Documenting here to help someone else in the future

Tom, the PDF on poly-v belts linked in the prior post is a treasure of information on belts.

A quick review of the document for maximum speed said that the poly-v belt design (at least from this company) can achieve speeds of up to 60/m sec, which I assume is meters per second.

A quick search of for a formula to convert meters/sec into RPM turned up this site of resources. https://lucidar.me/en/
The conversions are about 2/.3 down the page
https://lucidar.me/en/unit-converter/re ... er-second/

Assuming I am doing it properly, I entered the desired max speed of 10,000 RPM and a radius of .02 meters (for 2 centimeters?) the result is a meters per second of 21. So that is well within the rating for the poly-vbelt.

I will read up so I can find a match and then determine the pulley and belt I would need.

I'm very interested to know what belt design people are actually using for these speeds... Is everyone using Poly-v belts, or ....

[EricMack]

Here is a helpful belt/pulley calculator that lets you print the design and results and even print templates.

https://www.blocklayer.com/pulley-belteng.aspx

Now, I just need to find a suitable place to order the small pulleys and belts.

[tblough]

A few random tidbits to help:

I ended up making my own pulleys in order to get the ratios I needed.
Wider rib belts can be easily cut down into the number of ribs you need.
Fenner Trantorque keyless bushings are an excellent way to attach your pulleys to a shaft.
For 10K rpm you'll want steel pulleys.
For 10K rpm, you'll need to balance your pulleys and spindle.
Tapping balance weight holes in one of my custom pulleys.

[EricMack]

Tom, that looks great but its beyond my capabilities, so I'll have to look for something close to ready for now. Perhaps even XL Belts and just running at a slower speed, and then boot strap into something else. Thanks for sharing.

[mick41zxr]

I would second the vote for poly-v.
Also if possible I would recommend a tensioner pulley on the low tension side of the belt.
Thus will help reduce noise & vibrations when the spindle speed passes through any resonant speed (low tension side can do a great impersonation of a guitar string at times)

[tblough]

Unfortunately on a spindle (mill or lathe) there really isn't a low tension side since they can run in reverse as well.