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View Full Version : Changing collet type - obscure to common



jhovel
18th Jun 2016, 09:27 PM
When I got my beautiful Pear 3D pantograph mill, the 4 collets I got with it for its two spindles and tracer stylus were all broken to some extent. Replacements are hard to find and new ones were quoted at Eur152 EACH..... Their particular shape was not really conducive to making replicas either. They are inherently fragile.
One day, I noticed that ER16 collets had the same major diameter of the Pear collets for the high speed spindle and on checking further, ER20 matched close enough to the low speed spindle collets and the stylus.
So I firstly procured spare ER16 and ER20 nuts and a couple of cheap ER20 collets - I already had a full set of ER16s.
The Pear collets are a steeper taper than ER which meant that I was able to grind the holders to 8 deg to match ER standard.
The Pear collet holders are integral with the spindle and VERY hard. They also have fine threads (1mm pitch) - luckily larger than the ER nuts.
The next job was to bore the ER nuts to suit the Pear thread and cut M23x1 and M27x1 internal threads to match the spindles & stylus. They ended up coming out very well.
Working out a way of holding the stylus and spindles in my cylindrical grinder proved a failure, so I decided to do the internal taper grinding on my lathe.
I made a clamp/toolpost to suit my 55krpm air pencil grinder and bought a couple of CBN mounted points on 1/8" shafts.

So today I spent most of the day setting up my lathe topslide to exactly 8 degrees and set up the grinding spindle and drive mechanism.
The stylus was 'conventional': set true to the best of my ability (got close to 0.004mm indicated runout - not that I believe my test indicator, there would be more slop in the lathe spindle I would think...).
The Pear spindles are mounted on the same 'stalk' as the stylus, but belt-driven directly. So I set them true in the lathe, but drove them with a V-belt and DC motor clamped toa shef near the lathe. Lathe chuck standing still. That way there was no doubt about concentricity of my work.
I was a little disappointed with the amount the CBN points were removing, so I switched to mounted stones to produce the correct taper and used the CBN points to get the final finish. They were obviously too fine in grade.
However, all went well in the end with patience.....
I had to turn off a small amount of the threaded part of the ER clamping nuts, as the threads on the Pear spindles were shorter than the ER collet holders.

Original collets:
362845
Set-up for stylus:
362846
Progress and finish:
362847
Set-up for spindles:
362848
Result:
362849
Now I can get and use low cost collets in all supported sizes without breaking the bank...

Piers037
19th Jun 2016, 10:00 PM
Nice work Joe.

You have a real knack for modifying and repurposing machines to give them a new lease of life. Well done.

I have a few engraving jobs in mind, so I will be up to see you once I get back from my trip.

Cheers

Piers

Anorak Bob
20th Jun 2016, 09:56 AM
Another typical "Joe the Resurrector" project.

Fantastic work Joe, I really like the driven spindle setup. :2tsup:

Bob.

azzrock
2nd Jul 2016, 03:47 AM
Hi mate very funny I know people with those collets

jhovel
2nd Jul 2016, 11:47 PM
Hi mate very funny I know people with those collets

Too late, Arron.... Pity, but I've been looking for nearly a year now and found none under $150 EACH... Now I can buy a complete set for half that....

However, Joe Calvo, the guy I got the mill from, is still looking for collets for his Pear! Please put me in touch on his behalf by PM or phone.

azzrock
3rd Jul 2016, 12:09 AM
No problem joe. He has some very nice looking pear bits and peaces. My phone is dodging tax.(at the bottom of the harbour). So I have no ones number. I'll send a pm.