|Paul Ainsworth||06/04/2019 11:36:09|
|66 forum posts|
I recently bought a Jarvis Tapping Head from ebay, stripped and cleaned it and it is now running as it should. Does anyone know if I could fit a smaller collet insert to enable smaller taps to be used? Or is it a smaller chuck job? Smallest that will centre at the moment is 3/8".
|Clive Foster||06/04/2019 12:54:59|
|1670 forum posts|
Almost certainly yes to using different size collets if such can be got. But identifying the collet size and type will probably be challenging.
I believe Procunier and (some?) Ettco metal collets can still be bought new but there are a number of variants which rapidly get confusing. Fortunately most are obviously different when you look at the picture or drawing.
Tapmatic use a cone device that looks very similar to Jacobs Rubberflex, but much smaller. The inserts can be got for approaching £50 via MSC, example here **LINK** . Suitable holder looks like something that could be made at home, basically a conical receiving hole with a suitable screw on cap. Well into "how badly do you want this" territory.
All but the very smallest Pollard (licence built Ettco) heads have a simple chuck to hold the tap aligned. Looks just like the old style cheap hand drill ones. Three triangular jaws spring loaded apart in a screw-down cone. Does the deed just fine as the actual driving is done by the square.
Retro-fit may be possible if the existing drive end can be removed.
Simplest way is to make some tap carriers to fit the existing collet. If yours has a square driver that closes right up, like my Pollards, a simple split sleeve around the tap shank might suffice. Probably need to be afairly long tap tho'. Dunno that I'd care to go below 3/16 " or 5 mm with ahead that size tho'.
|Paul Ainsworth||06/04/2019 15:02:04|
|66 forum posts|
Just had a good look at the holding end, it's similar/same as your Pollard, 3 jaws and spring method to centre and square drive. Split sleeves sound like a good idea, if not I'll keep it for the bigger jobs.
|Clive Foster||06/04/2019 16:01:12|
|1670 forum posts|
Wonder how difficult it would be to make some more jaws that close up more. In principle same as what you have but wider and coming down thinner at the inside end ought to work.
Swopping over might well be a pain unless you can figure a way to hold the jaws together in the correct orientation against the springs whilst slipping them in. One of my Pollards had one distorted spring that stopped the chuck working properly. Finding a suitable replacement was bad enough but keeping three jaws and three springs aligned so as to slide into the cone needed verbal encouragement. Lots and lots of high power verbal encouragement.
One of my Pollards has been fitted an ordinary key type chuck instead of the proper driver unit. Which is pretty much useless. Looked into making a new end of proper style using a chuck off a big "gut buster" style hand drill. Then another one same complete with proper driver turned up at less than"wince" price so I bought that and figured I had the best of the bargain.
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