Chuck fitting

I have a BV20 (8 1/2” x 14&rdquo Lathe that uses 3 M8 cap head socket screws to secure the chuck to the lathe flange. The holes in the flange are counterbored. I’ve just noticed that some mini lathes use Hex headed bolts instead. I obviously can’t use them on my lathe due to the counter bored holes. I’m just wondering though if I could re-drill three new holes in the flange. It then occurred to me that if I do that I could maybe fit studs to all my chucks and then secure them with nuts instead. I have to say that the present setup using cap head socket screws is a bit of a PITA as there’s so little room the manufacturers supplied a cut down hex wrench for the job. Any thoughts? If you have a mini lathe how it the chuck secured?

I would do it and in fact I would probably prefer it. With plain bolts holding the chuck all of the registering will be done by the register. With countersunk head screws holding the chuck the self-centering function of the countersinks might be competing with the register for chuck alignment.

Counter-sunk, Pete? Vic says his lathe uses counter-bores, which are not self-centering.

I have a small lathe with similar fittings, not yet set up and used, and I've wondered how easy changing the chuck would be. If there is very little room it may be as awkward to manipulate nuts on studs as socket-screws, so altering it might not gain much.

You could just glue some spacers in the counterbores?, Or if you don't mind the faff and always losing them just have loose spacers.

If you would rather avoid drilling more holes in the spindle flange then I would do as Duncan suggests and machine up some spacers to match and fill the counterbores, although drilling three more holes won't cause a problem. 

I would then make them a light press fit, or glue them as suggested to keep them in place, and then use studs and nuts. If there is enough room behind the spindle flange it would be worthwhile machining a plain unthreaded portion on the ends of the studs, equal to about the length of the nut if possible and a snug fit , this lines up the nut with the stud threads and makes refitting them quicker and easier.

Edited By Lathejack on 16/07/2021 23:37:43

Edited By Lathejack on 16/07/2021 23:41:14

Edited By Lathejack on 16/07/2021 23:42:56

Ah, yes my apologies. What can I say it's been a long week...

Another couple of options:

Machine the tops off the cap heads a little. The hex recess will be shallower, but you are not tightening them to three grunts.

Investigate low head cap screws. They are a legitimate product, but more costly than standard capscrews.

If you look at YouTube videos of Cutting Edge Engineering Australia, he has a line boring machine. The heads of the cap heads holding it together face the thing being bored. They are in through holes, so he has made a screwdriver slot at the 'tail' end so the hex key is only needed for the last 1/4 turn, a (potentially power) screwdriver being used for the rest of the movement. It would mean converting the female threaded holes in the chuck to through holes, but they could be of a small diameter to suit the screwdriver.

Gluing the spacers in the counterbores means you need one spacer per counterbore per chuck. Gluing the spacer onto the securing nut means you need only one per fastener. If used on a nut and stud, it has the same benefit as the unthreaded section of stud suggested above.

3 more holes - no more faffing - gets my vote

I would go with spacers, as suggested by Duncan, in the counterbores. Fit studs to the chucks and use flange nuts to save faffing with washers. Works on my lathe!

John

Is there room to do a variant of the DIN 50527 mounting system? This has free rotating plate behind the flange with keyhole shaped apertures for bolts or studs. Bolt heads or nuts are small enough to pass through the holes in the flange and the round part of the keyhole. Rotating the plate brings the narrower slot under the bolt head or nut so things can be tightened up.

Obviously doing it properly with a round plate is impractical as you'd need to take the spindle out to fit it but given sufficient creativity and low cunning it ought to be possible to figure out something that could be installed. I'd probably make the plate in two parts overlapping at the ends with one joggled for the overlap so things fit flat. A little bit of glue under the joggles when fitted and it should stay together just fine as there is very little stress on the joint providing the plate is a running fit inside.

The real thing usually has a short dowel in the face of the flange projecting into the chuck backplate for a positive drive. Lets the bolt / studs be quite slack in the holes which makes assembly far easier.

The idea has been discussed a time or three on the forum before.

Clive

Some interesting ideas folks, thanks. I hadn’t thought about “filling up” the counterbored holes. It might work. The problem is there isn’t a lot of room behind the flange and you can’t see what you’re doing. Even measuring up could be difficult. If I decide to drill new holes cleaning up the back of them could be a faff. I’m really not interested in removing the spindle at the moment.

My inclination would be to follow Duncan's advice and to go for spacers, Loctited into the counterbores.

This would allow all chucks to be fitted with studs.

The risk of dropping muts during fitting and removal can be greatly reduced (almost eliminated ) by making up a DannyM2Z "Widget".

An extremely simple kit of kit that holds the nuts, whilst allowing access for a spanner.

Howard

You could, if there is room, make or buy 'shoulder bolts' similar to below:-

John

I’m not sure there is enough room behind the flange for something like that John, I’d need to check. I did think I could make some “Shoulder” nuts though. Might have similar problems with space though. I think it would help if I took some rough measurements and drew it out on the computer.

To minimise space, if you go down the shoulder nut route, the spigot for the counterbore does not need to be full length, just enough to locate the nut in the counterbore, so only 2 -3 mm.

IF you do do this, the "Widget" possibly may not function, in which case you have to be careful, not to drop the nuts, or to have some catchment (Cloth or tray ) ready for when they escape from your grasp.

(Last week found a nut that fell several months ago when I did not use the "Widget" )

Howard.

The counterbore seems to be about 13mm Diameter and 7.5mm deep. The hole through the flange for the 8mm bolts is about 9mm. Clearance for digits etc is around 20mm. I think I need a drawing!

If you have the space and really want to use different fixings, there is nothing to prevent you doing so. Look at this backplate being modified to take a smaller chuck. It looks a bit like a swiss cheese, but works perfectly.

I have a similar chuck mounting arrangement on my lathe. I had great difficulty manipulating the standard socket head bolts, too, not to mention the fiddly cranked allen key. I replaced them with hex head bolts with a threaded collar to bring the heads to the level of the rear face of the mounting flange. All this is a round about way of agreeing with John (Journeyman), above.

One thing I do to assist me, not having the benefit of three hands, is to clamp a piece of rod in the chuck itself and the tailstock chuck, bringing the ensemble up to the chuck mounting plate until the chuck engages with the register, leaving both hands free to fight the mounting bolts. Gently rotate the chuck until the holes line up and then insert the hex bolts. Start them off with your fingers and finish off with a spanner. I suspect many on here do the same.

It was published in MEW under "reader's tips" a long time ago, but I can't find it now.

John

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The shiny new MEW index suggests issue 248 … but it also spells your name incorrectly

MichaelG.

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Ref. https://www.model-engineer.co.uk/forums/postings.asp?th=173881

Edited By Michael Gilligan on 17/07/2021 21:21:16

Well done, Michael. That explains why I couldn't find it. And it wasn't a reader's tip, either! Not just the memory going, unfortunately.

John