Re: [CAD_CAM_EDM_DRO]spindle plans (was VFD Selection)

Hi Leslie;

Thanks for your posting. I do have a couple of questions though.

Why would you want to have the bearings pressed fitted to the spindle?
This seems like an unusual approach if you have a lock nut securing the
bearings inner races to the spindle. I've seen many a spindle built
with tapered roller bearings that had a press fit of the inner race, in
fact it is almost universal. On the otherhand it does not seem to be a
universal arraingement for angular contact bearings.

When I'm thinking about turning a ER collet extension into a spindle the
thought was to put the angular contact bearings near the collet end, add
a sleeve and then a ball bearing at the other end. All retained via a
lock nut threaded onto the end. Seems simple in my mind, with the
only machining requirements being the thread on the end.

What bothers me is the machining requirements for the outer housing.
At this time I'm of the opinion that getting the proper precision with
home shop tooling will be difficult.

I suppose that for low speed operation this would be fairly straight
forward. Getting good life out of a high speed spindle is another
issue. The question is at what point do you move away form preloaded
angluar conact bearign and go to externally loaded designs. The few
high speed spindles I've disassembled in the distance past where very
complex. What would you estimate to be the top end speed for the
arriangement you describe?

Short of finding a spindle cartridge cheap at an auction some place I do
not see an alternative that can be purchased. Prefabricated spindles
are awfully expensive.

Thanks
dave


Leslie M. Watts wrote:

>Since it will take me a while (crazy with work) let
>me go over some of the design concepts now.
>
>This is a thermally stable 3 bearing system.
>
>Near the work end of the tool there are two back-to back 25
>degree angular contact bearings adjacent to each other. These
>are supplied with the inner face slightly recessed (only microns)
>such that when they are squeezed together by a retaining nut
>a specific preload occurs (5% of max dynamic load). Further
>tightening of the nut does not increase the preload once the
>faces are forced into contact.
>
>These bearings are press fit on the shaft but a push fit on
>the housing. A shoulder and bolted ring secure the outer
>bearing edge. A shoulder formed on the shaft secures the inner ring, but
>it must be of a very specific size to allow bearing removal by
>pushing on the INNER ring only (with a special tool).
>
>The shaft has a short threaded portion for the retaining nut.
>
>Moving away from the tool end the shaft necks down slightly.
>This facilitates installing the angulars since they won't have
>to be pressed all the way down the shaft.
>
>At the back end there is another reduction in shaft diameter
>to provide a shoulder for press fitting a deep groove ball
>bearing. The outer part of this bearing will be allowed to
>float, but it will be very lightly preloaded with a Bellville
>washer to prevent ball scuffing. It is secured with a retaining
>nut as well.
>
>Thats basically it except for the engineering details.
>Pretty much a standard design that has been used for eons.
>
>Les
>
>Leslie M.Watts
>L M Watts Furniture
>Tiger Georgia USA
>(706) 212-0242
>http://www.lmwatts.com
>Engineering page:
>http://www.lmwatts.com/shop.html
>CNC surplus for sale:
>http://www.lmwatts.com/forsale.html
>CNC carved signs:
>http://www.lmwatts.com/signwp.html
>
>
>
>
>-----Original Message-----
>From: Vince Negrete [mailto:vnegrete@...]
>Sent: Wednesday, April 14, 2004 10:52 AM
>To: CAD_CAM_EDM_DRO@yahoogroups.com
>Subject: Re: [CAD_CAM_EDM_DRO]spindle plans (was VFD Selection)
>
>
>Les, Would it be possible to have a write-up/drawing on a site in PDF w/
>availability of a full kit?
>I'm primarily interested in design concept with exact specs/demensions to
>follow for building one from Stock.
>So far there are Several folks interested since last nights post.. :)
>
>Vince
>
>
>
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