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Thread: Chuck key
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13th Jun 2020, 12:25 AM #16Intermediate Member
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- May 2020
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- ACT
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- 27
If you want the original item they are available from Pratt Burnerd. I'm waiting for a price bit not expecting it to be cheap. I Imagine once I get a price and pick myself up off the floor I'll end up spinning one up out of some 20mm 4140 stock. Providing you have a mill it's not a major job to make one.
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13th Jun 2020, 06:36 PM #17
Hi Guys,
Pratt Burnard the chuck people are now part of the "600" group of companies !
I've just bought a replacement 100 mm three jaw chuck from ARC Euro here in the UK, the chuck key that comes with it is identical in size to the original PB one.
For the price I'm quite pleased with the quality of the chuck, the run out at the chuck jaws is less than 2/10 ths thou using a 20 mm diameter test bar and barely alters 150 mm away.
Unfortunately I can't say the same for the pre machined Myford fitting backplate that I bought from them some time ago. I originally bought it to put a ER32 collet chuck on it. The metal was coarse and rough to machine I couldn't get a smooth finish no mater how much I tried. I ended up grinding the surface to get a good finish. Also when drilling the three holes for the M8 cap screws it was like drilling stainless steel. Horrible stuff !Best Regards:
Baron J.
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13th Jun 2020, 07:35 PM #18Golden Member
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- Sep 2008
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- Riddells Creek, Vic.
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- 838
Hi BJ, are you saying that the Arc Euro chuck has a runout of .008"(0.2mm)? If so, it sounds a bit much, even for a 3 jaw.
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13th Jun 2020, 08:00 PM #19Most Valued Member
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- Mar 2011
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- Southern Flinders Ranges
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- 1,554
This is where things got to at the end of play today.. That and the discovery I can’t currently replicate the original flattened end of a Burnerd key on a piece of 10mm round bar because the hydraulics on my press are marking their territory too badly..
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13th Jun 2020, 08:29 PM #20
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13th Jun 2020, 09:01 PM #21
Hi Techo
Thanks for your post, I missed a "0" off the end. I've been back and corrected it. It gets confusing swapping between imperial and metric gauges !
I've re-edited it because I still got it wrong ! It should read two tenths of a thou ! I'm going to stop trying to come to terms with mm.Best Regards:
Baron J.
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14th Jun 2020, 05:35 AM #22
Getting it wrong !
Hi Guys,
I thought that since I had made a right pigs ear of measuring and reporting run out figures for my new ARC Euro chuck I would re-do the measurements and take some pictures as I went along.
13-06-2020-01.JPG 13-06-2020-02.jpg
I used a metric dial indicator this time so I couldn't get confused with thous.
This indicator is a 0.01 millimetre one. I started with an 8 mm diameter bar and rotated the chuck until the reading was the lowest nearest to the indicator. I then zeroed the indicator. I then rotated the chuck until the reading was a maximum.
In this case four divisions. (1.6 thou)
13-06-2020-03.JPG
Then I did the same with the 20 mm diameter test bar.
It only moved three divisions this time. (1.2 thou)
13-06-2020-04.jpg
Then I repeated the exercise with a 40 mm diameter bar.
Only two divisions this time. (0.8 thou)
I would have liked to try a bigger diameter say 50 mm but I don't have anything that big. It seems that the run out improves as the work diameter gets bigger.
So apologies for making a screw up in my original post. Thanks also to Lex for the prod to get it rightBest Regards:
Baron J.
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14th Jun 2020, 09:40 AM #23Most Valued Member
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- Nov 2007
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- melbourne australia
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- 3,228
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16th Jun 2020, 03:15 AM #24
Hi Chris, Guys,
Chris, I've used thous all my life but most on the forums seem to want measurements in millimetres. But yes you are right, trying to convert readings is causing confusion.
A few months ago I bought a HBM 125 mm three jaw chuck and back plate. I machined the register on the backplate for a nice snug fit into the back of the chuck. At this point I couldn't measure the jaws. Anyway after drilling for the M8 mounting holes and threading the back plate I mounted the chuck. On checking the chuck body there was about 10 thou eccentricity.
After having gone through measuring the new ARC Euro 100 mm chuck, I decided to do the same with the HBM one. Using the same setup as before, I had nearly 2 mm of runout with an 8 mm rod. This got worse as I moved to my 20 mm test bar.
I ended up machining a further 15 thou of the register and drilling out the M8 threads to 9 mm holes and use M8 cap screws from the back. This allowed me to tap the chuck central with a plastic faced hammer. I managed to get the run out down to 3/10ths mm with an 8 mm rod in the jaws. Even so the run out gets worse with increasing diameters. With a 45 mm diameter bar the run out is just short of a whole millimetre.
I believe that HBM is an Indian manufacturer. I certainly won't be buying another one.Best Regards:
Baron J.
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16th Jun 2020, 11:23 AM #25Most Valued Member
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16th Jun 2020, 05:56 PM #26Most Valued Member
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- Mar 2011
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- Southern Flinders Ranges
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Ready for the post office tomorrow..
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16th Jun 2020, 06:05 PM #27
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16th Jun 2020, 07:07 PM #28Most Valued Member
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- Mar 2011
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- Southern Flinders Ranges
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For the life of me I now have no idea where the key for my Pratt 3 jaw is
Cant be too far away, I used it to make yours
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16th Jun 2020, 08:34 PM #29
It’s there looking right at you! When you find it, you’ll say to yourself “ now I remember putting it there”.
I do that about twice a day.
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16th Jun 2020, 08:41 PM #30Senior Member
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- Jul 2011
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- Berowra Waters
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- 149
A file?
Maybe just buy a 10 mm and file 0.5 off each face? Wouldn’t take very long I would think.
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