DIY spindle design

[Jeremy]

I finished the mechanical part of the spindle today and gave it a test run. All went well, but I need to pull it apart and take a tiny skim from the lower bearing housing, as the lower bearing gets a bit warm after a few minutes running. I noticed that the spindle was a little tight after I assembled it. I hadn't realised how a tiny bit of "pinch" from a bearing pressed into a housing that was very slightly undersized would make such a difference, but it's easy enough to fix.

The good news is that the spindle is reasonably quiet and seems to work well off load. The RC motor didn't even get slightly warm, but the speed controller may need mounting on an additional heatsink, as it was a bit warm after a few minutes running. The motor was drawing around 10 amps from a 12V supply when running flat out, which is a bit high and almost certainly to do with the overly tight lower bearing.

I may also need to adjust the bearing pre-load. I've used a couple of belleville washers under the upper shaft retainer, abutting the top bearing inner race. Pre-load was set by clamping the shaft to compress the bellevilles a small amount, then tightening the shaft collar at the lower end. This wasn't very "scientific", so may also be a contributing factor to the warm running lower bearing.

Here's a picture of the completed spindle:



The body is 1.5" in diameter and the overall length is 8.75". The motor outer can at the top (the black bit with the writing on) rotates, so probably needs some sort of guard. The small lovejoy coupling seems to work fine, there's no real vibration at all with it spinning at full chat whilst just being hand-held. Overall it seems to vibrate a lot less than a Dremel and is certainly a lot quieter.

I've done a crude run-out check using a DTI, with it clamped in vee blocks on the surface table. A 3mm carbide cutter shank didn't seem to deflect the DTI at all, which seems pretty good. My DTI isn't really sensitive enough to show anything under about 1/4 thou though, plus the lower bearing is still a bit too tight, so the true run out might be a bit worse.

Nevertheless, if I can fix the lower bearing problem I think I shall be well pleased with this little experiment. Let's hope that the motor turns out to be reliable!

Jeremy

[miopicman]

I finished the mechanical part of the spindle today and gave it a test run. All went well, but I need to pull it apart and take a tiny skim from the lower bearing housing, as the lower bearing gets a bit warm after a few minutes running. I noticed that the spindle was a little tight after I assembled it. I hadn't realised how a tiny bit of "pinch" from a bearing pressed into a housing that was very slightly undersized would make such a difference, but it's easy enough to fix.

The good news is that the spindle is reasonably quiet and seems to work well off load. The RC motor didn't even get slightly warm, but the speed controller may need mounting on an additional heatsink, as it was a bit warm after a few minutes running. The motor was drawing around 10 amps from a 12V supply when running flat out, which is a bit high and almost certainly to do with the overly tight lower bearing.

I may also need to adjust the bearing pre-load. I've used a couple of belleville washers under the upper shaft retainer, abutting the top bearing inner race. Pre-load was set by clamping the shaft to compress the bellevilles a small amount, then tightening the shaft collar at the lower end. This wasn't very "scientific", so may also be a contributing factor to the warm running lower bearing.

Here's a picture of the completed spindle:



The body is 1.5" in diameter and the overall length is 8.75". The motor outer can at the top (the black bit with the writing on) rotates, so probably needs some sort of guard. The small lovejoy coupling seems to work fine, there's no real vibration at all with it spinning at full chat whilst just being hand-held. Overall it seems to vibrate a lot less than a Dremel and is certainly a lot quieter.

I've done a crude run-out check using a DTI, with it clamped in vee blocks on the surface table. A 3mm carbide cutter shank didn't seem to deflect the DTI at all, which seems pretty good. My DTI isn't really sensitive enough to show anything under about 1/4 thou though, plus the lower bearing is still a bit too tight, so the true run out might be a bit worse.

Nevertheless, if I can fix the lower bearing problem I think I shall be well pleased with this little experiment. Let's hope that the motor turns out to be reliable!

Jeremy

This is very interesting. I've already constructed a gantry type mill and am using a Kress router to mill non-metals. I'm now looking at ways of milling non-ferrous metals and manufacturing a spindle motor for this purpose. One component of the spindle I'm having difficulty sourcing is the actual spindle/collet holder - from where did you get yours please. I've sourced a suitable motor and have decided upon a step-pulley belt drive system in order to achieve good torque at low speeds.

[ChrisG]

Hi miopicman , has Jeremy used an air die-grinder as a base for his spindle?


http://www.screwfix.com/prods/38706/...ir-Die-Grinder

Chris

[miopicman]

Hi miopicman , has Jeremy used an air die-grinder as a base for his spindle?


http://www.screwfix.com/prods/38706/...ir-Die-Grinder

Chris

I don't think so; have a look at this: http://www.screwfix.com/sfd/i/cat/pdfs/89/p4764389.pdf