About a month ago, a fellow was selling some of his father's gear on eBay and amongst that gear was a 1/64 - 3/8" No.2A Erlach chuck. It was Swiss and unused and I was interested. A Google search revealed a suggested association between the Swiss firm Bergeon and Erlach, an eBay seller reckoned that Erlach chucks were supplied by Bergeon as accessories for their beautiful watchmaking lathes, and another seller said that Emco offered Erlachs as a more accurate drill chuck option for their Unimats than whatever their standard chuck was. And that was it.

The auction started at 20 dollars with a "buy it now" of thirty. I hummed and harred about dropping 30 bucks on an unknown so I placed a bid not long before the auction's end. I'd been outbid so another bid four seconds from the end made it mine. I mentioned the acquisition to my friend and fellow forumite, Piers and it was " ...k me!, you were the other bidder!! ". Had we both known a bit more about the chuck the seller might have been happier.

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My enquiries continued and after a post on the Schaublin Lathes Yahoo Group's site, I received some replies, one from William Brem who posted photos of a number of his Erlachs and suggested that Erlach may have been the original supplier of drill chucks to Schaublin.

William's chucks -

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The chuck arrived in the mail and it would not open. The application of some 3 in 1 oil managed to provide some movement but it was rough. I dismantled the chuck, cleaned, regreased and reassembled it and gave it a test mounted on a 1/2" straight shanked J2 arbor. The results looked promising, less than ''0.001 TIR with the arbor mounted in a 1/2" P20 collet in the 13's dividing head.

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To gain the greatest advantage from the Erlach, it needed to be mounted on a 12mm straight arbor which would allow its insertion in an ISO 30 collet. These collets do not project beyond the 13's spindle nose thereby saving precious Z. I toyed with the idea of making an arbor from 4140 but ended up pursuing the lazy alternative of modifying the 1/2" arbor. The downside of that option was the mutilated centre hole in the J2 end.

To remove arbors from chucks that won't accommodate wedges, Jacobs suggest drilling through the soft centre of the chuck and punching the arbor out with a drift through the hole. Invariably the arbor's centre hole is damaged. To reduce the shank diameter to 12mm it needed to be turned between centres because it would then be possible to grind it between centres. The mutilated centred required reboring. I used a Borite boring bar with has a cutting edge about 1mm in length. Worked well.

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Whilst I could grind the arbor, a comment Peter Fou made about it sometimes being easier to get close with the lathe then finish off with abrasive paper rather than fool around with the grinder stuck in my mind ( Peter sold me the Hercus tool and cutter grinder ) and that's what I ended up doing. The arbor is 12.00mm in diameter. The M6 tapped hole in the arbor's end is to facilitate its removal should the need arise.

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With the arbor securely mounted and the chuck in the 13's spindle , TIR is a hair over 0.0005". Not too bad for twenty nine dollars plus postage!

BT

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