ER16 8* taper = OK to use for QTC (ATC)?

[nicad]

I am wanting to modify an ER16 spindle into an Automatic Tool Changer capable spindle. I plan to machine holders that match the 8* taper to hold various end mills. I already have the internals of the spindle mostly planned out (using the typical clamping/locking/release of a ball joint on the top of each tool holder).
My question is, will the 8* walls give enough grabbing/holding power?
Second question- how many Lbs of force should I need to hold the tool holder firmly up into the spindle? Right now I am guessing on about 100lb, but really have no idea.

Any thoughts are appreciated.
Thanks-
Colin

[JFettig]

Hi, your 8 degree taper should work for most light work, possibly medium work. Youll want around 600 to 800 pounds of pressure, use belliville washers, for mine that I am ever so slowly working on I have some 400lb bellivilie washers I got from mcmaster.

Jon

[nicad]

Thanks so much for the direction. Now I know it wont be a destine-to-fail project (8* being enough for medium work). As for the holding force-- 400lb!! wow. how does one go about reliable compressing that much force? That would require a 2.5" diameter air ram at 85psi shop pressure to just barely break it over.. not to mention any progressiveness that the washers might have (i know its a small amount).

Any ideas on how to efficiently compress the springs/eject the holder? I know you do not want to apply that much force through your spindle bearings (it is just a Taig ER-16 spindle).

Thanks again-
Colin

[JFettig]

I actually have the spring washers doubled or trippled up, you can stack them parallel for more force or opposite for more travel.

I dont know what I am gonna use to push it, but so far I have just used a rod 7x multiplying my bodyweight

Jon

[RotarySMP]

Have you looked at:
http://home.insightbb.com/~joevicar3/default.htm
http://groups.yahoo.com/group/minitoolchanger/

This is a toolchanger based on an ER-16 spindle. His design uses 50lb of pull, and I asked Joe what his experiences have been. He can stall the sherline spindle without slippage.

He used the formula for conical clutchs from page 2243 25th edition machinery's handbook.

I have the sherline industrial ER-16 spindle on my mill, but haven't had time to finish the draw bar for it yet.

[JFettig]

Thanks Mark, this is giving me a whole different idea, with strait shank hodlers in collets I am giving them around that 600lb mark, with the retention nob kind of holders, it seems that it isnt needed?
I supose that 50lb is for a sherline with the little motor they throw on there, it could be slightly different with a larger motor taking larger cuts.

Jon

[RotarySMP]

Nicad has a Taig, which is in the same class as the sherline, so he sould be able to lean on the sherline experience.

I have a 1/2 Hp three phase motor with VFD driving the sherline industrial spible through a four step pulley, so the maximum torque at low speed can be pretty high. It will be interesting to see if I get any slippage once I make some tool holders and draw bar.