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View Full Version : Mini lathe - my first attempt turning plastic - useless!



HankMcSpank
02-09-2009, 11:48 PM
Hi there,

I've been quiet for a couple of weeks...it seems I didn't have swine flu a few weeks ago, but pneumonia resulting in a secondary complication - a lung abcess, so I've been in a North London hospital 'main lining' penecilin for 14 nights.

Anyway, after a fortnight listening to strangers coughing their guts all night every night, thankfully it seems the abcess is starting to shrink so they finally released me today.

In my opinion, their suggested bed rest is for complete wusses...nope, methinks "let's use this time wisely & start making stuff!" (the hospital have signed me off for two weeks :naughty:)

Ok, the story so far...I thought I didn't need a lathe, but then I realised I did, but I'm too tight to just go out & buy one, so I bought a non working lathe, then spent a week or so fixing it - it now works. That said, it doesn't have a chuck - I'm waiting on stock arriving from the far east...in the meantime I've bought an MT3 to MT2 Morse taper adapter which allows me to mount a MT2 drill chuck where the main chuck should be.

My goal today was simply to make a small V pulley wheel out of an existing small toothed plastic cog wheel (about 1.5cm Diameter, by 1cm in width).

So I mounts a cutting tool into the tool post & thought that my lathe would munch into the plastic easily...not a chance!

Now I don't know if it's my lack of experience, the wrong tool or perhaps aligned incorrectly (kip kindly gave me a load of cutting tools ...so I chose the one that looked like it would best recess a groove into the plastic), or maybe the fact that I'm using a drill chuck instead of a proper chuck (the plastic part I'm trying to turn keeps working loose of of the drill chuck jaws) or if my lathe is just woefully underpowered (it's an Axminster Sieg C2 with a 250W motor) ...the end result was that the tool barely scratched the suface...& this is plastic FFS!! (what hope do I have for shiny hard metallic stuff?!)

So I throw my plight open to the good forum - as a complete lathe noob, where am I likely going wrong?

I thought making these simple pulley wheels out of plastic would be an excellent 'intro' into using a lathe (& a doddle), but such was the frustration today that I'm now thinking lathes suck & pondering Ebaying it already!

John S
03-09-2009, 12:16 AM
Hank,
Although you have given us chapter end verse you haven't really told us a lot.
These thinks should cut plastic with no problems so something is wrong.

Can we have pictures ?

Stupid thing to ask but is the lathe going the right way, anticlockwise looking from the tailstock end.
Is the tool on centre hight ?

Is the tool sharp?
What's your PIN number.?

John S.

HiltonSteve
03-09-2009, 12:18 AM
Hi Hank, sorry to here about the pneumonia and hope you get back up to full speed soon.

So you can't even cut plastic on your lathe! That sounds as if you are doing something seriously wrong.....

Can you give us some more info on what cutting tools you are using, speeds etc and I will see if I can help, photo's would be good.

The drill chuck may not be helping you either but for turning plastic I thought that it would be good enough. You did have it rotating the correct way didn't you???:wink:

Just had a quick look on youtube and found the video below, just to show you that it should be possible to machine steel on your machine (not sure how accurate though looking at the video!)

YouTube - C2 lathe machining Steel

John S
03-09-2009, 12:46 AM
I have one of the little tiny C0 lathes, more of a toy really but handy for doing odd very small bits like screws and rivets.

As an example I made a new steel backplate for a 4 jaw chuck on it, 62mm in diameter by 15mm thick, other than the tapped hole everything else was done on this tiny lathe just to prove it could do it.
took quite a while and would have been minutes job on one of the bigger machines but it proved it can be done.

The C0 is about 1/3rd the size of what you have.

HankMcSpank
03-09-2009, 12:50 AM
Thanks for the prompt responses, I've just nipped up to take some pics (these are simulations as I'd thrown the part in the bin, but just retrieved it & remounted it to give you a flavour)

Firstly, this is an unfettered part that I want to turn a groove into (still in situ on an old printer)...

http://img181.imageshack.us/img181/1046/wheel1.th.jpg (http://img181.imageshack.us/i/wheel1.jpg/)

ok, here's the cutting tool I was trying to use...

http://img8.imageshack.us/img8/8440/lathe1.th.jpg (http://img8.imageshack.us/i/lathe1.jpg/) (my suspicion is now that it's too large which means the cutting tip is too far above the centre of the plastic part.)

The following is not a good photo, but I was trying to show where the cutting tip aligns when approaching cuting the part...

http://img17.imageshack.us/img17/447/lathe2.th.jpg (http://img17.imageshack.us/i/lathe2.jpg/)


this last photo is a 'rough up' of what I'm trying top achieve... actually that groove you see was done with a dremel & cutting disc as the lathe turned!

http://img17.imageshack.us/img17/3743/lathe3.th.jpg (http://img17.imageshack.us/i/lathe3.jpg/)


I reckon the following 'areas of investigation' can be ruled out...

1. Tool is completely sharp (it's a previously unused carbide tipped tool)

2. Motor direction ...I have the option of forward & reverse - I tried both directions!

Having pondered this a little bit more...I'm leaning towards that the tools may be a little large for my lathe's toolpost - they do fit in the tool post ok, but even to my untrained eye the tip of the tool is perhaps a little high (& probably the plastic part is being more 'ground' by the long downward edge of the cutting tool as opposed to being 'cut' by the tool tip!) . Like I say, I'm a complete 'wet behind the ears' with lathes...but hey, we've all got to start somewhere...& I started with plastic & ended up here!

HiltonSteve
03-09-2009, 01:20 AM
Having pondered this a little bit more...I'm leaning towards that the tools may be a little large for my lathe's toolpost - they do fit in the tool post ok, but even to my untrained eye the tip of the tool is perhaps a little high (& probably the plastic part is being more 'ground' by the long downward edge of the cutting tool as opposed to being 'cut' by the tool tip!) . Like I say, I'm a complete 'wet behind the ears' with lathes...but hey, we've all got to start somewhere...& I started with plastic & ended up here!

Yes, i would say the tool is too high.

Put a centre drill or something with a point on in the chuck and offer the tool up to it when mounted in the tool post, or you could use a centre if you have one for the tailstock. Tip of turning tool should be inline with the point or centreline of the drill or centre, too high and you won't cut a thing.

Edit - Found this which may help http://start-model-engineering.co.uk/

Lee Roberts
03-09-2009, 02:41 AM
(the hospital have signed me off for two weeks :naughty:)

Hehe, welcome back mate !

Robin Hewitt
03-09-2009, 07:09 AM
The tool is way too big, you want a smaller one. If the clamp doesn't have a vertical adjust you need lots of convenient sized shim to put under it for adjusting the centre height.

To cut a vee groove without CNC you might want to use the top slide set around at the correct angle so that the tool cuts on it's leading edge.

The world has gone carbide crazy, I think you want the slicing action you get from freshly ground HSS with relief angles front and top. It takes a much better edge. After grinding, round the sharp point off the end with a couple of strokes with a diamond hone, not so much as you can see without a microscope, and it will cut smooth rather than tearing the surface :beer:

BillTodd
03-09-2009, 02:16 PM
As Robin said, for plastic, use a HSS tool ground with large positive rake and lapped to a sharp edge.

To check the tool height quickly: gently clamp a 6" rule or similar strip of thin material between the work piece and the tool - It should be vertical if the height is correct. If the top of the rule leans away from the tool the tool is too high, if the top leans towards the tool the tool is too low.

and by the way

NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK NEVER LEAVE THE CHUCK KEY IN THE CHUCK
NEVER LEAVE THE CHUCK KEY IN THE CHUCK

even on a mini-lathe ! it is a bad habit to get into.

[edit] You might be able mill a mm or two off the bottom of Kip's old tools to make them usable in your mini lathe, if they're not too high in the holder.

BillTodd
03-09-2009, 02:35 PM
You might want to have a look at MIT lathe and workshop videos.

http://techtv.mit.edu/videos/144-machine-shop-8

HankMcSpank
03-09-2009, 02:49 PM
Thanks guys...I'll give it another bash later with the suggestions posted up here.

Now off to watch those Videos!

PS Bill - point taken about leaving the key in the chuck! In my lame defence, it was late & I just wanted to get some rough & ready photos posted up here (the lathe wasn't even plugged in when the photos were taken!). As it goes my lathe has a chuckguard that is meant to close a safety switch when in position - problem is I got the lathe in a state of disrepair & the chuckguard switch mechanism was lying loose in a box - I can't for the life of me see how the switch can be closed by the chuckguard - so for the time being it's overridden...but I will pencil in a trip to one of the Axminster stores soon, to see if I can eyeball how the darned thing gets actuated by the chuckguard. I realise it's a golden rule & I'm actually paranod about it - far better to have a failsafe like a chuckguard switch which will protect my cheek from being embedded with the key (that said it might get me a couple more weeks off work)

HankMcSpank
04-09-2009, 10:01 AM
Yes, i would say the tool is too high.

Put a centre drill or something with a point on in the chuck and offer the tool up to it when mounted in the tool post

Just to give some closure here, it is indeed a misalignment problem...

http://img200.imageshack.us/img200/715/lathef.th.jpg (http://img200.imageshack.us/i/lathef.jpg/)

it's only out by a margin of something approaching six weeks! (ie not even close!)

Looks like I'm gonna have to get some smaller tools.

Thanks everyone ...hopefully some good came out of this thread (ie those videos for others that are clueless like myself!)

BillTodd
04-09-2009, 02:23 PM
Looks like I'm gonna have to get some smaller tools.

Looks like a 10mm or 3/8" tool. You'd have to go down to 1/4" (which are feeble little things) to fit that tool post. Generally, there's no disadvantage using a bigger tool, so if you can find a way of mounting them, use them.

If I were you, I'd have a close look at the tool-post mounting to see if you can reduce its height by 4-5mm (even if it means getting some material machined off the bottom), it'll give you greater flexibility in the choice of tool.

If you can find a cheap quick change tool post, it may allow you a greater range of vertical adjustment, plus you get the advantage of easy tool height setting FOC.

HiltonSteve
04-09-2009, 03:07 PM
Looks like a 10mm or 3/8" tool. You'd have to go down to 1/4" (which are feeble little things) to fit that tool post. Generally, there's no disadvantage using a bigger tool, so if you can find a way of mounting them, use them.

If I were you, I'd have a close look at the tool-post mounting to see if you can reduce its height by 4-5mm (even if it means getting some material machined off the bottom), it'll give you greater flexibility in the choice of tool.

If you can find a cheap quick change tool post, it may allow you a greater range of vertical adjustment, plus you get the advantage of easy tool height setting FOC.

I completely agree...!

I would strongly suggest changing the toolpost for a quick change system like this one - http://www.arceurotrade.co.uk/Catalogue/Machines-Accessories/Lathes/Model-C3-Mini-Lathe/C3-Quick-Change-Tool-Post-Set

It will make life so much easier for you.

Robin Hewitt
04-09-2009, 04:23 PM
NEVER LEAVE THE CHUCK KEY IN THE CHUCK

But if your key comes fitted with a spring to stop you leaving in the chuck, remove said spring before it drives you banyanas :beer:

BillTodd
04-09-2009, 09:48 PM
But if your key comes fitted with a spring to stop you leaving in the chuck, remove said spring before it drives you banyanas :beer:
Absolutely, they're a daft idea - the sort of idea H&S people come-up with!

HankMcSpank
04-09-2009, 11:18 PM
Thanks chaps ...time to splosh a bit of dosh by the looks of it.

(Bill...'casing the joint' ...there's no way I can get that tool post lower - I can only hope that a quick change toolpost wins me back a bit of real estate below the tool post.)


As it goes, I'd previously tried to wrap my head around how/why a quick change tool post would be so benefeical (though the name of it is a bit of a giveaway!), but I can now see that lining the tool up is likely to be a major time sump.

In the end to make the pulley wheels I needed for my homemade coil winder, I milled them in 'halves' them on my homemade CNC - then glued them together! The edges were a bit rough so I tidied them up on the lathe using a wood chisel & a tool bit (I kid you not). It worked, but my oh my...what a laborious way to get some pulley wheels. Yes, I know....pulley wheels only cost coppers, but I couldn't find them in the sizes I wanted (& I wanted them today!)