Spindle Choice - VFD or Sherline?

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brw0513
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Spindle Choice - VFD or Sherline?

Post by brw0513 »

My CNC router table is coming along. Time to think about the Z axis and choose a spindle.

The router will be mostly used to cut model helicopter sideframes out of 1.6mm fibreglass and aluminium sheet. There will also be some brackets out of 6mm aluminium plate and perhaps an exhaust gasket made out of 2mm stainless steel.

I have been thinking about a 0.75kW 24,000rpm VFD spindle like this:

http://www.arceurotrade.co.uk/Catalogue ... -Inverters

But have a Sherline ER16 10,000rpm spindle:

http://www.sherlineipd.com/spindles.htm

With the Sherline spindle, I'd use a T5 belt and pulley drive arrangement with a 240V AC motor out of a 2kW electric blower with its crude variable speed controller.

The VFD spindle is a nice solution, but not sure how capable it would be at slower speeds if my duty would require it.

The Sherline option would be heavy and limited to 10,000rpm but may be the better choice.

I'd like some good advice on which way to go.

Thanks.
Ian B

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metalworkz
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Re: Spindle Choice - VFD or Sherline?

Post by metalworkz »

Hello,
It might come down to how much torque you need for the work you plan on doing. The variable high speed spindles seem to be pretty popular and will probably work well for wood and similar items, but if you plan on working much with metal then you may opt for the Sherline or a Taig spindle setup which possibly will provide more torque at the lower RPMs for those types of work. I do a lot of aluminum cutting with my CNC mill and CNC router but am in the process of making a better alternative for the router when cutting aluminum. I have to keep the depth of cut and feed rates down cutting aluminum with the rotozip spindle in the CNC router and am tentatively working on a different spindle setup for cutting aluminum. It should enable deeper cuts and better overall capabilities and I have been looking at a Taig spindle and motor or something similar of my own making to accomplish this. I feel the high speed spindles will not give me the needed torque for cutting aluminum, but I don't have any real experience with them to offer.
Best regards,
Wes
wes.spence@comcast.net
Gingery Machines:
Lathe, Horiz. Mill, Shaper, Leaf Brake

brw0513
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Joined: Fri Apr 20, 2012 10:25 am
Model of CNC Machine: Router
Location: Brisbane, Australia

Re: Spindle Choice - VFD or Sherline?

Post by brw0513 »

To get a feel for the Sherline spindle at speeds up to 10,00rpm I made up a belt drive "jig" today. The gear ratio was a bit taller than ideal - just selected on the T5 pulleys I had available. I didn't adjust the bearing preload, but the spindle sure got rather hot after just a few minutes. And the combination of motor and spindle was rather heavy.

I've decided to further pursue the VFD arrangement.

The advice I've received from DamenCNC.com about the C31/40-C-SB-P-ER20-0.7KW-18000RPM TeknoMotor HF spindle has been terrific. If they can satisfy me about warranty and a few other questions, then they deserve my business.
Ian B

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Adrian
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Re: Spindle Choice - VFD or Sherline?

Post by Adrian »

What's the minimum rpm the spindle can go down to without losing torque?

brw0513
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Re: Spindle Choice - VFD or Sherline?

Post by brw0513 »

Adrian wrote:What's the minimum rpm the spindle can go down to without losing torque?
Adrian,

I don't know for certain. My assumption is these spindles would not be very useful at speeds less than 10,000rpm.

I have a theoretical article here somewhere about brushless motor power and torque theory. If I can find it, I'll post it.
Ian B

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Adrian
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Re: Spindle Choice - VFD or Sherline?

Post by Adrian »

The spindle I use has an effective range of 8k to 18k rpm. Was thinking that if yours works in a similiar range then you're not going to be able to go below 14k which might be too much for the materials you're cutting.

brw0513
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Re: Spindle Choice - VFD or Sherline?

Post by brw0513 »

Adrian,

What spindle do you have, what material do you machine with it and at what speed and feed?

I admit I have lots to learn about routing, but I would have thought well chosen carbide end mills of 3mm dia and less would thrive on 18,000rpm in sheet aluminium and fibreglass. I thought the real trick would be matching the feedrate to make sure the tool was not under/overloaded. But happy to receive any good advice to save me learning a hard lesson or two or three :)

The chap at DamenCNC I have been swapping emails with has been very helpful and has used the HF motor I mentioned earlier for the duties I have described. I intend to send him a final summary email to confirm his recommendations against my requirements, then place an order.
Ian B

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Adrian
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Re: Spindle Choice - VFD or Sherline?

Post by Adrian »

Ian, I'm no expert on metal or fibreglass for that matter most what I machine is wood, MDF and plastics. It's rare I cut anything at much over 14k and I use feed rates of between 3 and 6 ips. My spindle is an HSD 2.2 as supplied by ShopBot.

The need for the low RPM's was more of a gut feeling based on the ali machining my father-in-law does with hand power tools. I must admit that after doing a bit of research into it I can see that it's a confusing area. There are people cutting ali on CNC's who are running routers at 24k and swearing they're getting perfect results and others cutting at 10k saying the others must be smoking something!

One thing that does seem to be consitent amongst those reporting good results is the use of single flute cutters.

Good luck!

dan_barber
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Re: Spindle Choice - VFD or Sherline?

Post by dan_barber »

My choice would be a VFD because of all the different options/functions. I currently have a Hitachi drive.

http://www.clrwtr.com/Hitachi-WJ200.htm

brw0513
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Re: Spindle Choice - VFD or Sherline?

Post by brw0513 »

Thanks for the responses again :)

After thinking about this some more, I only really want my router to be good at making model heli frames - prototypes out of 2mm plywood with the final version out of 1.9mm epoxy fibreglass sheet.

So I'll shelve the idea of the aluminium and stainless on this machine. The near future needs for items out of those materials could be handled by a small manual milling machine anway. I'll keep my eye out on FleaBay.

It seems the bests bits for routing fibreglass are really burrs. I had my cursor hovering over the "Buy Now" button the other night, but will wait until I hear back from a burr supplier to confirm speeds and feeds before placing the order for the spindle and VFD.
Ian B

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