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Thread: Brass bearings.
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13th Sep 2019, 10:41 PM #1
Brass bearings.
Hi Guys,
I need some advice !
13-09-2019006.JPG 13-09-2019005.JPG 13-09-2019004.JPG
I've been trying to make some bearings. The pictures show what I've been making !
My issue is whilst holding these in a square ER32 collet block, they are moving and causing the faces to be machined at an angle. I thought that the collet was not tight enough and have tried with a 12" inch wrench to tighten them further, but they still slip round. This is my third lot and is probably the best of the bunch.
The threaded bit is 8 mm in diameter and 10 mm long, the head is 10 mm thick and 18 mm diameter before putting the flats on.
Help !!!Best Regards:
Baron J.
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13th Sep 2019, 11:09 PM #2Most Valued Member
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- Apr 2012
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Hi John, maybe fill the hole, you could try tightening a cap screw in them and they might hold tighter with less distortion/flex/crush in the collet.
cheers, shed
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13th Sep 2019, 11:18 PM #3
Hi John,
Thanks for your reply. OK I'll try that ! It hadn't occurred to me that the collet might be crushing the brass.
I will report back.Best Regards:
Baron J.
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14th Sep 2019, 05:22 AM #4Senior Member
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Lighter cuts when machining to reduce the force?
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14th Sep 2019, 06:02 AM #5Most Valued Member
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10 mm is not very much to hold going into a 30mm long collet, they may just be too short for the collet to grip correctly.
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14th Sep 2019, 07:39 AM #6Philomath in training
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I agree with Peter - the spigot you are holding is not long enough. Screw a piece in to the spigot to extend it or add a loose piece so that the collet has equal diameters along it's length (or at least at both ends) and you will be able to hold it much more firmly.
Michael
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14th Sep 2019, 07:07 PM #7
Hi Guys,
Thank you very much for your replies and very useful suggestions ! Now that you have pointed things out it now makes a lot of sense to me.
I propose to use a long cap screw and put an 8 mm extension piece screwed on behind the bearing bush. I'll do this today, I can turn down one of the scrap pieces to make one 20 mm long. I did look inside the collet and there is a 30 mm long section without any breaks, so nothing at the back end.
I will report back, thanks.Best Regards:
Baron J.
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14th Sep 2019, 08:29 PM #8Golden Member
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- Apr 2009
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- Ballina N.S.W.
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Baron J
Extending the grip length will help with the holding. I have found by wrapping the diameter with a piece of 600 wed & dry paper with the grit side bearing on the shaft can increase your hold. Are you milling the flats working parallel to the longitudinal axis and taking light cuts?
Bob
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14th Sep 2019, 10:27 PM #9Senior Member
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- jilliby nsw
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Hi, I would place a couple of machinist jacks under the first milled flat to support the work and stop it rotating. Agree with the others that their is insufficient material in the collett to grip the work tight enough. The othewr option is machine the first flat then place the work in a small vice and in some parallels , then machine the second flat. Hope this helps
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14th Sep 2019, 10:44 PM #10Gear expert in training
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This.
With so much of the collet clamping air, when you tighten it you are going to crush the back of the collet and flare the front so you only really have a ring of single point contact on the end of the part (you also risk permanently deforming the collet). The minimum recommended clamping length is 2/3 the collet length, so an extension or filler should sort it out.
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14th Sep 2019, 11:15 PM #11Senior Member
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- jilliby nsw
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Yes I agrees with what you say elanjacobs re collett grip length. If I were to make these I would turn the blanks in the lathe and then mill the flats using a fly cutter or similar whilst holding the work piece in a machine vice.
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15th Sep 2019, 12:45 AM #12Senior Member
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- Aug 2007
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- Saskatoon, Saskatchewan, Canada
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I would consider cutting the flats on a long bar and hold it in the lathe with the 4 jaw. Do all the turning and threading and then part to length. Advance the bar and repeat.
Pete
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15th Sep 2019, 03:41 AM #13
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15th Sep 2019, 03:46 AM #14
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15th Sep 2019, 04:02 AM #15
Hi Guys,
Many thanks to all for the helpful and useful suggestions. I'm still learning
The job is now done. I hadn't understood just how much brass can move under pressure, particularly when clamping what was effectively a thin wall tube.
14-09-2019=006.JPG 14-09-2019=005.JPG
This how I got the problem sorted. I turned one of the bad bushes so that it was an 8 mm diameter M6 threaded tube. I put a bolt through and screwed the tube onto the bolt so that it provided more material for the collet to grip.
14-09-2019=001.JPG 14-09-2019=002.JPG 14-09-2019=003.jpg
This is how I set up the collet and collet block. Put the whole lot in the mill vise and carefully machined the flat on both sides. I also machined a small flat on one end to make it easier drill a 1/4" hole through it.
So success ! I can now carry on with my Brooks TCG.
Thanks again guys.Best Regards:
Baron J.
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