Beginner question - facing off in a lathe.

Hi all,

I'm a newbie to machining and still experimenting with my lathe, I've only had it a few days and still at the 'swarf making stage'.

At the moment I'm trying to face off the end of a steel tube approx. 40mm in diameter and with walls about 6mm thick. The results I'm getting look reasonable given that I'm a beginner and it's scrap steel till my purchase of better stock arrives.

The only slight worry I have is the ends are poorly cut at an angle so when I have it properly aligned in the chuck and begin facing my tool initially bangs against the high spots (which are prob 5mm higher than the lows)

It doesn't seem to bother my 8x16 machine but to a newbie the banging is a bit disconcerting. Is it anything to worry about ?

I tried initially making very fine cuts but found it seems to cope better taking bigger cuts and feeding faster.

I realise I could part off the ends but if I was wanting to preserve as much of the material as possible is there any problem facing badly cut ends ?

Many thanks

Peter.

It might be that you are using the cheap carbide tipped tools. These don't cut well. Don't worry about the noise. As long as the tube isn't moving in the chuck it's ok.

Move in with the compound slide so it's more controlled or take short, tiny cuts along the diameter

Don't use a parting tool on an intermittent cut as the blade is likely to push off.

You'll soon work out what works best.

Edited By Capstan Speaking on 02/06/2015 12:45:56

As a rule interrupted cuts are okay. If you are using carbide then you need to take more care as it is quite brittle and may chip. Round off the corners of tools (or use an insert with a bigger tip radius ) as sharp points lack strength. If you proceed with caution (it sounds like you are) then you should get a feel for what is right. Obviously being to aggressive with feeds or speeds will end up with broken tools or worse things whistling past your ear. So make sure that the work is securely held.

Good luck.

David.

Hi Peter

I know you know I am a beginner like you - so take my comments in that context!

I'm a bit of a mother hen when it comes to my equipment and I like to minimise wear and tear as much as I can. If there is 5mm difference, then I say hacksaw, file and then a light cut in the lathe - probably quicker on a little lathe as well - and its only a tube to cut through..

Banging is not good best to reduce that kind of use to a minimum on your new kit...

Cheers

Garry

Thanks guys, I'm using a carbide tipped tool at the moment, It's very much a steep learning curve when you are new to this. I'm still experimenting with positioning the tool at slightly different angles as well as different speeds and feed rates.

To be fair once I got past the intermittent cut stage I was pleasantly surprised with how my first attempt looked

Interrupt cuts should not be a problem, same occurs when you have a casting or some other shaped part in the lathe.

I tend to use auto feeds where ever possible as my lathe has auto feed on the saddle and cross slide this has the advantage of always taking the same amount per rev even fresh air, if you do not have auto feed then remember air is very easy to machine so don't be tempted to speed up a nice constant feed is what is required.

Bob

Interrupted cuts are of course sometimes / often necessary - I have already learned that decisions can be made to minimise them though - it makes sense to do so when you can Peter. This sounds an obvious example of being able to do that..

Having one bit of metal banging into another not good on any precision machine - why do it when you don't have to!

Garry

Edited By Gary on 02/06/2015 13:58:30

Steel tube,particularly tube rolled and seam welded,is the worst of the common materials to machine,its tough and stringy, On a small lathe I would use a hss tool with small tip rad and 20 degree top rake, and feed the cross slide by hand, when feeding by hand you can feel how the tool is cutting and if it is about to dig in the feed can rapidly slowed or if necessary stopped or reversed,if using power feed by the time the the stop lever has been operated the tool will have dug in, with jobs like this its patience not speed thats required.Now if you had a heavy lathe like a colchester triumph with 40 mm tube held in a big 10 inch chuck the method would be ,use big carbide or hss tool and feed the saddle towards the chuck cutting the entire 6mm width,it would knock a bit but that does not matter, when close to the finished length,lock the saddle and take a finish cut by facing with the cross slide to ensure face is square to the axis of the tube. I recently squared off 30 lengths of scaffold tube like this on my triumph,horrible material but thats what the customer required.

Hi Peter Nichols

You did not mention how much of the tube is hanging out of the chuck.

A 6mm wall tube is quite thick so you can get away with a fair projection without the risk of the tool digging in and dragging the tube out of the chuck and maybe whizzing past your ear if you are lucky.

Ideally the work should just project out of the chuck far enough for the tool to easily clear, on thin work a few mm on thicker work maybe 20mm

If the work is projecting more than its diameter I like to take it easy and back of the feed.

If ever you can actually see the work springing (moving away from the tool) as it turns you are pushing the feed too far. Unpleasant loud noise often accompanies this.

Often the work is too thick to pass through the lathe mandrel and we have to work with excessive overhang, when doing so take extra care. Or better still use a steady rest whenever possible to support the work.

Regards
John

Edited By John McNamara on 02/06/2015 14:16:55

Many thanks for all the helpful replies.

As I'm only practising and not yet working to any precise dimensions I would guess the work was maybe about 50 - 60 mm out of the chuck (on about 40mm diameter tubing) it seemed very solidly held and didn't move or slip.

I agree its not the best metal to work with as a beginner and I have ordered a supply of better materials from an online hobby metals supplier. (hopefully they'll arrive tomorrow).

Really I'm still very much learning even the basics of which tool to use, what angle, what speed etc without trying to cope with difficult materials.

On a job like yours I have found that starting from the chuck side and working out to the end often works better. Start on a complete round part and work towards the rough bits. Try and keep the feed constant, difficult with intermitant cuts.

I think your being a tad over-cautions Gary. Even the bearings on my mini-lathe are bigger than those on most cars, and while the latter aren't used for high precision metalworking, they do have an expected life of over 200,000 miles of continual battering.

A well-adjusted lathe should be quite happy with interrupted cuts, the issue is when slides or bearings are loose - then things flap about and can get damaged.

Neil

Hi Neil

Its very good to hear you say that, reassuring in fact because it comes from someone who obviously knows - it will serve to lesson my 'cringe' factor quite a bit when I'm having to do it..! There are of course different levels here though - some materials and situations I've found are no problem whatsoever..

I would always try to minimise mechanical impact when I can though, that's all I've been trying to say - if its not possible to do that then ok the job has to be done but if there's an easier route for my machinery I would always take it - as I've always done with all the other types of machinery I've used - and its served me well..

I must have a very sensitive mechanical soul..! Good to have your thoughts though...

Cheers

Garry

Thanks for the help guys,

My order of materials has now arrived and I've just had quick go at swarf making to see how aluminium and steel rods behave, thankfully it's a vast improvement machining better quality stock than the scrap yard steel I was practising with.

I also happened to snap the spindle holding the knob on one of my saucepan lids, so it looks like making a new one will be my first ever 'proper' job

Peter

A brass saucepan lid knob with thread and nuts was my second 'proper' job, so touche

Edited By Ralph H on 03/06/2015 13:34:03

I would sugest putting the CT tooling in a draw, and learn to use HSS, this will be adequate for 90% of the work, and you can easily shape and sharpen your tools to suit the job. Steel pipe such as the bit you are having a go at is horrible stuff, but can be usefull, the cylinder of one of my oldest Stirling Engines is made of it, it's run a bit over a 1000 hrs, and shows no sign of wear, so it's worth learning how to get a good finish on even this sort of C**p.

Here it is, built not long after I got my lathe.

Hi Ian,

I've given up on the steel pipe now that I have some better materials to work with.

As for the tools I'm going to buy a bench grinder in the next few days and once I have one I'll get myself some HSS, I only got my machine on Friday and the carbide tools came with it so I thought I might as well give them a go.

Peter

Peter, bear in mind that Tipped tooling always needs to run about 150% faster than HSS! HSS has a sharp edge and a good degree of clearance whereas Tipped tooling has very little clearance and its cutting action is more like shearing the metal, it also requires more power which may not be available in a small lathe. There is also a degree of rigidity required to absorb all this deflection.

Definitely go on to HSS and learn to grind the correct clearances for the cutting edges, do that and your reward will be good finishes and less problems.

Keep the tipped tools for hard metals etc.

Clive

Thanks for that Clive, I wasn't aware tipped tooling needs to run at faster speeds.

I've read up a fair bit about tooling but I'm still very much at the stage of putting the tool in and seeing what happens !