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Hi there I've just gotten myself an old unimat selecta mini-lathe, with the standard 3 jaw chuck installed. I seem to be having quite a bit of trouble 1. getting things centred and 2. getting the jaws to hold my part properly. With soft aluminium of course, the non-centred thing isn't so much of an issue as I just start bigger and work my way down in size, however when it comes to machining steel I can't for the life of me take virtually any cuts without the part catching the binding up the motor, and then coming out of the chuck jaws. I must note I've changed the motor from the standard 70-watt one over to a 150-watt electric scooter motor. Is it possible to do something to my chuck to make it centre parts better and be able to hold on to them easier or is it a case of getting a new chuck. 4 Jaw perhaps? I am using some cheap carbide lathe tools off eBay if that helps at all (I've ordered some indexable carbide tools with the tcmt tip on to replace these in the hope this helps me out a bit)
Any help is greatly appreciated as this is a whole new world to me and I'm trying to learn as I go.?
Thanks Dan?
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Hi
A couple of things. Are the jaws in the correct slots, they are numbered.
Do the jaws have any sign of wear.
Could you show us some photos of the chuck so we can get a better idea.
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It may well be the jaws are not in the correct positions. There are numbers stamped on the jaws and on the body, maybe check?
Cheers, James,?
Locked down in Dunfermline, Fife, UK
Hi there I've just gotten myself an old unimat selecta mini-lathe, with the standard 3 jaw chuck installed. I seem to be having quite a bit of trouble 1. getting things centred and 2. getting the jaws to hold my part properly. With soft aluminium of course, the non-centred thing isn't so much of an issue as I just start bigger and work my way down in size, however when it comes to machining steel I can't for the life of me take virtually any cuts without the part catching the binding up the motor, and then coming out of the chuck jaws. I must note I've changed the motor from the standard 70-watt one over to a 150-watt electric scooter motor. Is it possible to do something to my chuck to make it centre parts better and be able to hold on to them easier or is it a case of getting a new chuck. 4 Jaw perhaps? I am using some cheap carbide lathe tools off eBay if that helps at all (I've ordered some indexable carbide tools with the tcmt tip on to replace these in the hope this helps me out a bit)
Any help is greatly appreciated as this is a whole new world to me and I'm trying to learn as I go.?
Thanks Dan?
-- James Batchelor
This email contains recycled electrons
--
James Batchelor?
Dunfermline, Fife, UK.?
07805 207238
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Hi, and welcome to the group.
3-jaw chucks vary in runout, but should not be as bad as you describe unless something is wrong. Like poorly fitted backplate.
But you mentioned centering the workpiece. If it is round or hex, obviously you use the 3-jaw if it was set up properly for minimal runout (meaning correctly machining the backplate on the lathe it is used on).
The 4-jaw can be used with any shape for centering manually.
-----Original Message-----
Hi there I've just gotten myself an old unimat selecta mini-lathe, with the standard 3 jaw chuck installed. I seem to be having quite a bit of trouble 1. getting things centred and 2. getting the jaws to hold my part properly. With soft aluminium of course, the non-centred thing isn't so much of an issue as I just start bigger and work my way down in size, however when it comes to machining steel I can't for the life of me take virtually any cuts without the part catching the binding up the motor, and then coming out of the chuck jaws. I must note I've changed the motor from the standard 70-watt one over to a 150-watt electric scooter motor. Is it possible to do something to my chuck to make it centre parts better and be able to hold on to them easier or is it a case of getting a new chuck. 4 Jaw perhaps? I am using some cheap carbide lathe tools off eBay if that helps at all (I've ordered some indexable carbide tools with the tcmt tip on to replace these in the hope this helps me out a bit)
Any help is greatly appreciated as this is a whole new world to me and I'm trying to learn as I go.?
Thanks Dan?
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Hi there?
I've been trying to centre just round peices of steel and aluminium but just having too much luck, I also don't know anything much about machining or this lathe, so I have no idea what I'm doing just trying to work things out. ?
Also I cant seem to find much out about the selects model the most common seems to be the sl and dB series and I'm not sure how similar they are ?
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- light cuts
- sharp tool with approx correct rake for the material
- approx correct speed for the material
- support at the tailstock end if the material is say greater
than 3 times longer than its diameter or 3 times longer than the
jaw
- use the tommy bars to clamp the work firmly in the jaws (1/8"
Meccano aka Erector rods are about perfect of you don't have the
originals)
The 3-jaw chuck won't centre precisely unless you are very lucky,
so until you've taken some metal off all round, it will cut on one
side and not the other - so use *very* light cuts at first else
the tool will bang onto the metal and stick until it is cutting
all round.
Maybe I'm not a beginner anymore !
On 06/04/2020 16:46, Daniel via
groups.io wrote:
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Hi there?
I've been trying to centre just round peices of steel and
aluminium but just having too much luck, I also don't know
anything much about machining or this lathe, so I have no idea
what I'm doing just trying to work things out. ?
Also I cant seem to find much out about the selects model the most
common seems to be the sl and dB series and I'm not sure how
similar they are ?
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Not 100% sure on the speeds but even with the lightest of cuts with my current tools just stopped the part dead and binds up whilst dislodging it in the chuck or removing it completely. I'm still not sure how to angle the tools correctly for the different materials , any guidance you could give me would be greatly appreciated ?
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You say you are using cheap carbide tools, are they the brazed tip type that are color coded?
I find them to be pretty bad. They just aren't sharp enough. For small lathes the cutters need to be razor sharp. Better with HSS or ccgt type indexable tips. Blunt cutters will rub rather than cut, you should check they are on centreline too. This could be your problem.?
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Yes at the moment I'm using some of the braised tip cutters , when I ordered them I wasn't sure on what I needed and they were a decent price to start l. I've ordered a set of indexable tools with a tcmt tip on them am I likely to have more luck with those ? The tools are on the centre line I took the chuck off and put the dead centre in the spindle and lined the tool up like that. Is that a good way of doing it ? If not how should I go about it ?
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G'Day!
I am using tungsten carbide cutters, on all of my lathes, including the D-bed Lorch (which is as flimsy as they get) without any trouble. Of course I do not use Chinese TC cutters, I make my own from broken TC centre drills or from the broken solid carbide drill bits 1/8" in diameter, I made several holders out of key steel holding TC bits in with a 3 mm set screws. The TC bits I grind with diamond wheels in my tool and cutter grinder. Had no problems whatsoever, cutting hardened and tempered steel like butter. The HSS cutters I use mainly for brass and other non ferrous alloys and metals, sometimes I use HSS cutters with addition of cobalt on some steel parts.
Cheers, Dushan
You say you are using cheap carbide tools, are they the brazed tip type that are color coded?
I find them to be pretty bad. They just aren't sharp enough. For small lathes the cutters need to be razor sharp. Better with HSS or ccgt type indexable tips. Blunt cutters will rub rather than cut, you should check they are on centreline too. This could be your problem.?
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Selecta is just a one-time branding of the SL/DB:
Marketing was then taken
over (at an unknown date) first by "Selecta", an established and
much larger purveyor of small tools, as the? "Selecta Universal Metal
Workshop" and
then by one of the country's largest machine-tool manufacturers
and agents "Elliott Machine Equipment Ltd." as the "Elliott Universal Machine
Tool".
On 06/04/2020 16:46, Daniel via
groups.io wrote:
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Show quoted text
Also I cant seem to find much out about the selects model the most
common seems to be the sl and dB series and I'm not sure how
similar they are ?
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You are centering them up correctly and yes that is a good way of doing it.?
Ideally you want tcgt tips, they are designed for finishing non ferrous (aluminium and brass) but they work well in small lathes and will cut steel.
The tcmt tips you have ordered will likely be better than the braised tips but not optimal imo. I won't try and explain why because it's a subject that is quite huge and in depth. But basically its tip geometry, speeds and machine rigidity.?
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On Mon, Apr 6, 2020 at 06:46 PM, Unimat Matt wrote:
You are centering them up correctly and yes that is a good way of doing it.?
Ideally you want tcgt tips, they are designed for finishing non ferrous (aluminium and brass) but they work well in small lathes and will cut steel.
The tcmt tips you have ordered will likely be better than the braised tips but not optimal imo. I won't try and explain why because it's a subject that is quite huge and in depth. But basically its tip geometry, speeds and machine rigidity.?
?Is it worth investing in some of those aswell or see how I go with tcmt ?
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Brilliant good to know makes my life a bit easier when looking for parts?
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Hi Dan,
These are very small lathes, with low powered motors, flexible bed
and corresponding chuck clamping capabilities.
As Mehmood pointed out, a sharp tool is an absolute must (along with
light cuts).
If you look with a magnifying glass at the tip of your "cheap
carbide" tool, you will most likely find out that it is not very
sharp.
Try to use HSS toolbit, with properly sharpened and honed cutting
edge. Use very light cuts.
With the old motor, you would probably stall the motor before
ripping the part out of the chuck.
Now with the new more powerful motor, you found the next weak link,
chuck holding capability.
Forces exerted on the chuck are greater with the new motor (assuming
all other conditions are the same, the work piece material, speed
and depth of cut, same tool), motor does not stall anymore and this
greater force exceed chuck holding capability.
What I am trying to say is that perhaps there is nothing wrong with
the chuck, it is just not capable doing what you are asking it to
do.
If you are machining small diameters, maybe a collet chuck would
work for you.
But if nothing else changes (i.e. using sharp tool, lighter
cut...etc.), then you will find the next weak link of Unimat lathe,
the flexible way bars.
The tool will be simply pushed away from the work piece.
Roman
On 2020-04-05 6:52 p.m., Daniel via
groups.io wrote:
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Show quoted text
Hi there I've just gotten myself an old unimat selecta mini-lathe,
with the standard 3 jaw chuck installed. I seem to be having quite
a bit of trouble 1. getting things centred and 2. getting the jaws
to hold my part properly. With soft aluminium of course, the
non-centred thing isn't so much of an issue as I just start bigger
and work my way down in size, however when it comes to machining
steel I can't for the life of me take virtually any cuts without
the part catching the binding up the motor, and then coming out of
the chuck jaws. I must note I've changed the motor from the
standard 70-watt one over to a 150-watt electric scooter motor. Is
it possible to do something to my chuck to make it centre parts
better and be able to hold on to them easier or is it a case of
getting a new chuck. 4 Jaw perhaps? I am using some cheap carbide
lathe tools off eBay if that helps at all (I've ordered some
indexable carbide tools with the tcmt tip on to replace these in
the hope this helps me out a bit)
Any help is greatly appreciated as this is a whole new world to me
and I'm trying to learn as I go.?
Thanks Dan?
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Try the tcmt first. I am just guessing at your original problem dont forget.
A couple of other things I would do in the meantime which might help your chuck runout.
.Clean all the swarf from the chuck.
.Make sure the backplate and the mating surface on the spindle don't have any raised burrs.
. Make sure the spindle and chuck threads are spotless before screwing the chuck on.
Its quite unbelievable how even the smallest particle of swarf can throw out the accuracy.
Another thing you can check for is "bell mouthed" jaws. Put something very round and hard metal like a big drill bit or milling cutter in the chuck and hold it up to the light. If you can see a lot of daylight between the clamped object and the jaws then that can be a problem.?
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I'll give that a try, is there anything do if the jaws are bell mouthed or is it toast at that point ? Are the soba 4 jaw chucks a better than the three or are they useless ? Any suggestions on a 4 jaw chuck or something.
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I bought an aftermarket 4-jaw chuck, but rarely use it.? When I do, its
for different reasons, occasionally to get something more precisely
centered, but even then it is more reliable to turn up a one-off
purpose-cut collet-type of holder drilled and tapped to the 12mm spindle
thread.? Mostly the 4 jaw is to hold a quadrilateral bar or irregular
item that won't hold in the 3 jaw. I use my 4-jaw more often to hold
something offset in the tailstock, e.g. a crank hole when the piece is
clamped in the tailstock and not on the cross-slide.? It probably came
from Chronos or RDG Tools in the UK, I forget.
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On 06/04/2020 19:37, Daniel via groups.io wrote: I'll give that a try, is there anything do if the jaws are bell
mouthed or is it toast at that point ? Are the soba 4 jaw chucks a
better than the three or are they useless ? Any suggestions on a 4 jaw
chuck or something.
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Les Orton
James Batchelor
Unimat Matt
Roman Gargulak