|Tom Laughran||21/10/2019 14:38:59|
|1 forum posts|
Just wondering if anyone can help me with a query I have..My colleague at work has a Holbrook Model B No. 8 Lathe and he needs to mount a Pratt Bernard 3 jaw chuck on to it which he has. We know that the thread size on the nose is 1.3/4" BSF but we need to make or buy an adaptor plate that will fit the nose thread so that we can mount the chuck. Does anyone have any suggestions how we go about this. Maybe someone has already fitted a chuck.
|Martin Johnson 1||21/10/2019 16:41:37|
|129 forum posts|
If you have access to another lathe, the job is fairly simple. Some of the well known traders sell backplate and faceplate generic castings. It will help if the Holbrook spindle is available (i.e. dismantled) for fitting the threads and registers on your casting.
If you don't have access to another lathe, you really need to start with at least something that already fits on the nose - this can be a faceplate or a catchplate for between centres work. Have you tried the usual 2nd machinery dealers for something?
Assuming your Holbrook is now armed with a faceplate / catchplate the routine is drill, tap and screw your chuck backplate with boss pointing toward tailstock onto the facaplate. Now machine the thread and register - you will have to unscrew the whole lot to check thread fits and registers - a pain, but possible. Once you have a thread and register done, remove the backplate, screw it onto the spindle nose and machine the face and spigot for the chuck.
I hope that all makes sense.
|357 forum posts|
Don’t think you will have much luck with a casting, I certainly couldn’t find one big enough on the boss dimensions. Best bet is get a slice of steel or cast iron off a bar. Largest chuck you can usefully use on the B8 is five inch diameter. A 1-2 micrometer and bore gauge is all you really need plus ideally a plug tap just for use as a gauge, not for tapping the thread with. When I done mine I done it on the B8 and held the billet in the 4 jaw, screwcutting was easy using the lathes screwcutting stop. Certainly would not dismantle the spindle just for this job, unless you intend totally rebuilding headstock.
|Clive Foster||21/10/2019 17:12:04|
|2157 forum posts|
The Holbrook spindle has two parallel registers, one in front of the thread and one behind. Unique with the 1 3/4" BSF thread so no chance of finding a new, commercially made, one. Very unlikely to find a second hand one as these machines were rare, being very expensive new. Even if you do find a used one it may well not fit. It is said that Holbrook fitted backplates individually to each spindle.
You will need to make an accurate dummy spindle for final turning / fitting and, probably, an accurate pair of size gauges for the registers first. You can do the registers by measurement but final fitting gauges generally make it easier to get it right. Sounds the long way round but I've found that properly setting up with a dummy spindle end makes the job go far faster even with ordinary threaded spindles. Never done a Holbrook one tho'.
Best to have practice run on some spare material first. Although its fundamentally simple work getting it right needs concentration. The back register in particular being a pain if not approached correctly. I imagine the auto feed stop on the Holbrook will help if its still in good order.
Be highly tempted to make more than one backplate when set-up and in the groove.
PS I see Baz did his without a dummy spindle. Well done mate. Braver man than I.
Edited By Clive Foster on 21/10/2019 17:13:43
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