New Lathe - poor suface finish on my results

I've just received my new Axminster C2 lathe and have been playing.

I'm super inexperienced, so possible I'm making some horrendous mistakes, but so far I've been a little disapointed with the surface finish I've been seeing.

I purchased some nice EN1A steel from ebay - my googling showed that that was the best steel to use for turning. I also purchased some HSS tools as well as some indexable tools and have been experimenting with both. I've been using short run out, with the workpiece sticking out about 6 or 7 cm from the chuck.

My experiments so far have yielded pretty poor surface finish, it's grainy and bumpy - even when I take super light passes. Thus I have concluded I must be doing something wrong.

Other aspects of what I'm seeing are:

- I think there is some backlash somewhere - when I take a light pass towards the chuck. At the completion of the cut, when I move the head back towards the tailstock, it's still cutting which I thought was odd (e.g like the cutting head is moving slightly towards the work when I start to traverse back)

- Not really sure what speeds to use (despite googling) - for a 12mm dia bar, I'm up near the top of the lathes speeds and that's where I seem to get better results.

- I've tried with and without lubricant, and it seems much the same.

Grateful for any advice people have to offer.

Hello Ace,

Although I'm not qualified to offer specific advice regarding your questions, I can possibly save you some time, by suggesting you take and upload some photos.

You will certainly be asked this by the more knowledgeable folk here, and, as always, a picture tells a thousand words.

Good luck and HTH.

ATB,

Daniel

Super light passes are your problem. Super light passes require super sharp tooling, if you can't shave with it it's not sharp enough. Insert tooling is generally blunter than well sharpened HSS. but either way the tooling needs to be cutting not rubbing. The tool also needs a slight radius on the tip to avoid a very fine thread being produced.

This online calculator will help with starting values for speed and feed. Try values either side of them and see how your machine handles them.

Speeds and feeds calculator

Try a depth of cut about 0.2mm for testing purposes.

Back off from the workpiece at the end of the pass to return to the start for the next pass.

Martin C

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@Martin - Thanks a lot for the feedback. Based on that calculator, I'm going too fast on the speed I think.

The two most common causes of poor finish are the material and the tooling. So I'd make the following points:

Don't buy material from Ebay unless you know what you're doing and don't care about finish. The quality of material varies widely even for nominally the same specification. Proper EN1A is one of the more forgiving steels and should give a good finish.

HSS tooling should produce a good finish, but is dependent upon how it is ground. You do not need fancy guides and setups to grind HSS (I hand grind my tools) but the shape needs to be roughly correct with proper clearance.

Insert tooling can be fussier about cutting conditions. It's possible that a small lathe simply won't have the speed and power to get the best from inserts. The same caveat applies to inserts as to materials; cheap inserts may not perform as well as more expensive branded ones.

A stick out of 60/70mm without tailstock support is quite ambitious on a small lathe.

Recutting on the way back to the tailstock is normal, even on industrial lathes. It's due to work and tool deflection, and the cutting process itself. It will become second nature to simply withdraw the tool, wind back and reset the tool position.

For HSS tooling and 12mm diameter EN1A I'd be running at about 800rpm (100 feet per minute surface speed). For insert tooling you can easily be three or more times that.

Andrew

1. Check that every gib is adjusted to get a slight drag. Don't expect the manufacturer to have adjusted everything to the best fit. Loose fitment on the cross slide and compound will get you bad results.

2. Sharp tools make accurate cuts. Dull tools push the steel instead of cutting it. Carbide inserts have their place. They are made to be able to withstand higher temperatures that come with high RPM and heavy feeds. They cannot be super sharp because they are brittle and the edge will chip. If you want super sharp so you can make very light cuts use high speed steel and learn to grind the proper shape and to hone it to razor sharp.

3. Back off the tool from the steel before backing the carriage for the next cut.

A photo of what you are getting is a bigger help. And what tooling you are using as well. Then more accurate advise can be offered. There are some carbide inserts that are very sharp these days. They work well on lower powered home hobby lathes. The very sharp inserts are made for cutting plastics and Aluminium. But do work very well on steels with light cuts. Sometimes you need a small nose radius to reduce deflection and tool cutting pressure.

Sometimes the poor surface finish comes from other factors, like vibration from the motor or belt drive system etc.

So no one answer to the problem. A photo can help to eliminate the various options.

Nothing wrong with hss steel and learning to grind and hone your own tools. Sometimes a shaped piece of hss is the best option , especially for forms or repeating short length tapers etc

Neil

At this time in your experience,10 minutes with someone showing you how and why on your lathe will save weeks of guessing. However many books and videos you watch and read.

i know it goes against the grain a bit, but, its well worth it. we were all beginners once, and we still make mistakes, but we dont tell anybody anymore

best of luck

could you help me understand a bit more what the first point precisely means? - does "slight drag" mean that it should feel a little tighter than one might intuitively think was needed?

Don't know what the Axminster manual is like as I couldn't find a link on their website to download it. Here is a link to the Grizzly version.

Grizzly mini lathe manual

See page 34 for gib adjustment (I don't know if the g is like the first g in garage or the second g in garage, I have heard both used).

Consider the carriage like a rectangular block in a vice. If the vice is wide open then the block can be rotated in the horizontal plane between the jaws. As the jaws are closed together the available space for rotating is reduced until there is none and the part is held tightly. If you want to move the block from left to right or right to left you need to loosen the vice slightly. The carriage has got to slide on the ways, if it is too tight it will not move, if it is too loose it will try and rotate just like the block between the vice jaws. On a lathe there is a sweet spot that balances able to slide with acceptable rotation, that is what adjustment aims for. There must always be some give in order to allow parts to slide.

Backlash on a lathe is something completely different and, for the most part when manual turning, can be ignored.

Martin C

Various comments, the first as |i climb aboard one of my hobby horses.

Is the tool sharp? AND is it on the centre line?

If it is not it will, not cut properly. Too low and you have excess clearances. Too high, and the tool does not cut, it rubs because the cutting edge is above centreline, and cannot contact the work..

Tool overhang from the toolpost should not be any more than is necessary. The longer it is, the more flexible it is. And rigidity is important. A tool that is waving about in the breeze is unlikely to produce accurate work.

This is why industrial machines are massive, heavy and rigid.

A quick check for tool height, if you do not have a Centre Height Gauge (Easy to make) is that when the tool faces the work, (Cuts across to machine the end of the bar )and reaches the centre, there should be no "pip" evident.

If you want to see a picture of a centre height gauge, and instructions on how to make one, PM me, with an E mail address..

For what my advice is worth, start off with High Speed Steel tools, and learn how to grind them.

You may think that is worth investing in some books.

"The Amateur's lathe" by L H Sparey is old but a good starting point, tending to centre around the Myford ML7. But the principles are good, neverthe less. There are other books on Lathework by folk like Harold Hall, Neil Wyatt, Dave Fenner and so on. They may not all feature your particular lathe, but the basic principles are the same.

Neil Wyatt recently wrote a series of article on basic lathework, in Model Engineers Workshop. It featured the Sieg SC4 lathe, which is a big sister to your S2 (Neil is one of the many users of the SC2 lathe, and his book will feature it )

Carbide tips are not sharp. They were intended for heavy duty industrial machines to remove lots of metal, fast!

A good all purpose tool for turning and facing is a Tangential Tool (On another hobby horse! )

You can make your own. There have been at least two designs published in M E W, (for 1/8" toolbits )or you can buy the Diamond Tool from Eccentric Engineering. I have made several, ( for 1/8 and for 5/16" toolbits ), for myself and for others, including The WaterWorks Museum in Hereford.

What feed rate are you using? A fine feed would be about 0.004" (0.1 mm ) per rev of the chuck.

Too coarse a feed rate will produce a rough finish. You are effectively cutting a screw thread, of sorts!

You will always have backlash in the machine movements, otherwise nothing could move.

The machine is new, so backlash should not be excessive. If it ain't broke; don't fix it!, You might make things worse!

Whereabouts are you located?

Hope all this rambling is of some help

Howard

Snug up the gib while trying to turn the handwheel. Do each gib screw and make sure the screw is slightly snug but does not bind the handwheel. The handwheel should still turn relatively easy but not freely. Hard to explain better without being there.

Would have to agree with all of the above advice, Reason ? Have been there-done that-ruined the tee shirts !

Overhang from chuck is too much

Tool always cuts on the return stroke, that,s why you need to retract it

Forget about inserts at this stage, HSS is all you need to get perfect finish, easy to grind, cheap to buy.

Speed is easy to work out, most books give detailed info on it, Sparey mentions 80/1/4 of work dia= revs. all gone Metric now, but the idea is the same.

Tool needs to CUT, not rub, so centre height needs to be right

You think you have problems now ? Wait till you get to parting off !!!!!

One last thing ,keep in mind the size of your machine, it is not a factory monster tipping the scales at ten tons.

I made a little progress and some improvements here.

1. Bolted down the lathe to the bench, it was moving a little, I suspect that the vibrations weren't helping

2. Making more use of the power feed. the hand feed isn't geared, so it moves too fast if you turn with the handle on the wheel, therefore you have to turn the wheel with your hand, I think when I readjusted my hand position for the next bit of the turn, I was getting little lines as the tool was paused for a while. I'm sure I could develop some two-handed technique so it doesn't stop while I adjust hand position - but using the power feed seems to yeild better results.

3. As advised here, I'm taking slightly heavier cuts, which yields better results.

I'll try and video the set up so that people can see and observe if there is anything else that's obvious that I'm doing wrong.

I think when I readjusted my hand position for the next bit of the turn, I was getting little lines as the tool was paused for a while. I'm sure I could develop some two-handed technique so it doesn't stop while I adjust hand position

Do try using two hands on the handwheel - you can continue the feed when one hand gets to the limit with the other, which allows you to re-position the first hand to take over when the second runs out of travel. Do this with all the feed handles - takes a bit of practice, but becomes second nature after a while.

Does get a bit tedious facing a faceplate when you don't have power cross feed, though.

Nigel B.

One of the first things that I was taught was how to provide a steady hand feed.

Practice makes perfect, so that one hand takes over the drive from the other without stopping.

A valuable skill, that will be needed quite often in the future.

If you are using power feed, use the finest that you can get, about 0.004" (0.1 mm ) per rev, or less.

A rigidly held, and correctly centred, sharp, (correctly ground ) tool is necessary starting point.

Don't practice on rebar; it is vile stuff to machine. Learn on some free cutting mild steel.

."Unknownium" can cause all sorts of problems, without admitting to being the cause!

Howard

Yes, I bought some EN1A from ebay (per previous post on here, I at least *think* it's EN1A).

I've played with some turning down some bolts (M10 ones that I had to hand), but I don't think I'd try rebar

M10 bolts are a swine to machine, particularly 8.8 grade. Even on an ex industrial machine, it is very hard to get a decent finish.