Chuck backplate

This topic has 13 replies, 9 voices, and was last updated 24 July 2016 at 14:01 by not done it yet.

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23 July 2016 at 11:05 #247723
MW
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@mw27036
I was machining a backplate to fit a new collet chuck but the problem is i've gone 0.3-0.4 mm over the ideal size of 100mm on the register flange and is it worth saving? I've kinda given up and suspect the only other Way i could hold it is in the four jaw, but wondered what everyone else thinks.

Michael W

Edited By Michael Walters on 23/07/2016 11:05:27
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23 July 2016 at 11:05 #24654
MW
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@mw27036
23 July 2016 at 11:06 #247724
Nick_G
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@nick_g
.

Is there enough thickness in the plate to take a facing cut and try cutting the register again.?

Nick
23 July 2016 at 11:09 #247725
MW
Participant
@mw27036
Ah yes, there might be, I didn't cut the male flange to it's full thickness of 8mm simply because it's too way too much, so it's only 3mm deep, but it's a good fit nonetheless. That is a way i could do it, cut again and deliberately undersize the female dia. on the first pass, then creep up to full size?

Michael W
23 July 2016 at 11:33 #247731
JasonB
Moderator
@jasonb
The other option is to leave it undersize which with give you the option to knudge the internal taper of the collet chuck true should there be any error in it's machining. You can then tighten up the mounting screws and add a couple of dowels so it won't move again. Sort of poor man's Griptrue.
23 July 2016 at 11:33 #247732
Nigel Bennett
Participant
@nigelbennett69913
I've made several backplate registers on my lathe undersize by 0,5mm or so. That way you can nip up the securing screws on the chuck/collet holder and bop it to run true using a DTI and a soft hammer.( I will leave it to you to decide how these implements are used…)

Nipping up the screws tightly should ensure it stays reasonably true – but the DTI/mallet system does allow you to make adjustments to any job you have, a bit like a cheap Griptru.

Only thing to watch is if you have a big dig-in, which might cause the chuck to slip slightly and hence eccentric running. You just have to get the mallet out again and take shallower cuts!

(Jason got in before I'd finished typing!)

Edited By Nigel Bennett on 23/07/2016 11:34:23
23 July 2016 at 12:31 #247744
MW
Participant
@mw27036
Sorry guys. They do sound like good ideas but i've just gone and tried to machine undersize and because my boring tools are low quality and big radius on the end it just makes any kind of cut follow the existing groove rather than cutting a new one because it's that close to size.

I could buy another casting one day and have another go at it but for now, the collet chuck is only 125mm O/D and that means i can grip it in the 4 jaw. That should allow me to adjust it to perfection provided the interal collet taper is sound to begin with. I guess it'll have to wait til i clean up and find out.

My interest in this is mainly because i have alot of plastic to machine these days and all of it is under 25mm.

Speaking of which, can anyone recommend some decent boring tools (mine a brazed carbide) like sandvik or something?

Michael W

Edited By Michael Walters on 23/07/2016 12:33:09
23 July 2016 at 12:51 #247746
Nick_G
Participant
@nick_g
Posted by Michael Walters on 23/07/2016 12:31:13:

Speaking of which, can anyone recommend some decent boring tools (mine a brazed carbide) like sandvik or something?

.

Go to 'that' auction site and search 'Iscar boring bar'

Nick
23 July 2016 at 13:11 #247751
Bazyle
Participant
@bazyle
Don't understand how the "existing groove" works as I am imagining something like a chuck backplate with a recess instead of protrusion. At 5 in dia and 3 mm deep you could use a regular HSS knife tool not a boring tool. As it is not load bearing perhaps painting Araldite around the recess would hold enough to allow another try.
23 July 2016 at 13:31 #247758
JasonB
Moderator
@jasonb
As Bazyle says just grind a bit of HSS does not have to be a boring bar something like a trepanning tool will do nicely.

Also a bit confused by the "groove" a pic would help

All my insert tool holders are Glanze/ARC, if you are machining plastic get some **GT tips

Edited By JasonB on 23/07/2016 13:33:53
23 July 2016 at 14:44 #247766
Raymond Anderson
Participant
@raymondanderson34407
Michael, As Nick G said just go to e bay and type in boring bars. You will find plenty of good makes. Sandvik, Iscar, Kennametal ect I even managed to find a brand new Walter 32 Ø one for about 75% of the price of a new one. Not sure of what size of lathe you have but up to about a 16mm bar seems to be a good upper limit size for models. although there is no definitive size, all depends on what you need it for and what your lathe can accommodate.

I can never have enough boring bars, all styles up to 40mm Ø which is me largest one [only needed to use it a few times up to now ]

Cheers
23 July 2016 at 15:12 #247769
Ajohnw
Participant
@ajohnw51620
It makes a lot of sense to make a plug gauge first and creep up on that. They are not the easiest thing to use at this sort of diameter. A very short lead that goes in fairly easily helps as before the rest fits it will square it up.

You ideally want a rather light press fit.

I'd use a HSS tool as well.

Lol – I'm referring to fitting a plate to the lathe – not the chuck. Fitting to the chuck is easier as it can be checked before cutting the full length of the dia and some faced off when it's correct.

John

–

Edited By Ajohnw on 23/07/2016 15:16:14
24 July 2016 at 11:19 #247853
Ian S C
Participant
@iansc
Stick the carbide tool back in the draw, for light finishing cuts you need a HSS tool, the carbide tool in a boring bar in a light lathe is sure to take off too much if you are looking for the last thou or so.

Ian S C
24 July 2016 at 14:01 #247875
not done it yet
Participant
@notdoneityet
An early mistake, when making a back plate was that of measuring while 'warm'. A spot on measurement, and cut carefully to size, ended with a loose fit when cool. Lesson learned. Luckily it was for a four faw chuck, so perhaps not quite so important…. as long as the fasteners do not come loose.
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