Looks like that is the finest feed you are going to get on that lathe with only one stud for a gear pair between the reverse tumbler and the leadscrew. Compare it with a Myford that has two adjustable studs on a forked banjo that allows for two pairs of reduction gears between between the reverse tumbler and leadscrew. Probably all you could is look for a smaller gear to go on the tumbler reverse output.

But poor finish could also be a result of poor toolbit, worn bearings, worn bed, job sticking out too far from fhe chuck, worn chuck, or even a duff bit of material. If you are using Chinese brazed carbide toolbits, they will need sharpening before use.

Also if your carbide tools are 'as bought' they may well be not sharp and even have no clearance. Some of the tools in sets do come unfinished and I think there were some photos on a post here recenty.
It sounds like you may be a woodturner so find an old 1/4 in mortice chisel, prepare it with only 15 degree bevel and instead of top rake raise it 1mm above centre, you should be able to get it in the tool clamp even with the handle still on. Just to see the difference.

Edit. Now I've looked at the photos that tool looks like carbon steel, not carbide or HSS. It may have lost its temper at the end.

Edited By Bazyle on 05/07/2020 10:49:35

En3 is not generally known for its machinability, you can get a good finish on it but you would have to be a bit more fussy in everything being 'right' than for En1pb as noted above. As to 3" protrusion from the chuck, that depends on the size of the bar. 3/8" bar or smaller sticking out 3" would tend to ride up, can be done but sharp tool and light cuts are the order of the day. A lump of 3" bar, fill your boots, take as big a cut as your motor will drive 3" from the chuck! It's not only the rigidity of the machine that determines what you can do, you also have to consider the work piece.

It's all part of the learning curve.

Paul.

Good news – you know what the steel is! Here's what's said about EN3B's machinability, my bold:

EN3B can be machined at reasonably high speed with moderate feeds; although machinability is relatively easy it should be noted that surface ripping is a common problem unless an adequate lubricant is used during the machining process.

And:

Therefore, it is the weldability of EN3B that defines its use – if good weldability is not a consideration and greater machinability is required then a free cutting steel such as EN1A should be considered as an appropriate alternative.

So, EN3B isn't a good steel for beginners to start with on an unknown lathe. It may well be the guilty party, which is good news.

An adequate cutting fluid might be:

• Water (avoid due to rust)
• Lard, or Milk (best not, milk stinks and both cause infected cuts)
• Cutting Oil, as used for screw-tapping CT90/Rocol/etc or one sold specifically for machining steel.
• 3-in-1 or a clean plain motor oil (not the usual car type full of additives)
• Cutting oil made into an emulsion with water 'SUDS' The water evaporates leaving a film of oil behind and it doesn't cause corrosion like water.

For cleanliness, I use either CT90 (pricey), or neat cutting oil, or plain Lawnmower oil, or similar. Although I bought a flood cooling system, it's rarely used. A mug full of liquid and keeping wet with a brush is good enough. Be careful not to splash coolant on to a carbide cutter because it tends to crack due to thermal shock. Either brush the work away from the cut or flood the whole lot continuously.

Although Lard, Sunflower Oil and additive packed motor oils are best avoided in the long run, not much harm will be done trying them provided they're cleaned up carefully. Paint the job with what you have available and try again.  3-in-1 works OK but it's smelly.

Dave

Edited By SillyOldDuffer on 05/07/2020 14:59:20

Comments that may or may not be valid.

1 ) The tool needs to be sharp (Carbide is not really sharp compared to HSS ) The lathe was made before carbide tools were conceived, so I would recommend using sharp, HSS tools. The tools need to have clearance (about 5 – 10 degrees ) in all three planes. Front, side and top – usually known as " top rake. )

Your lathe is not suitable for the speeds and feeds needed to get the best from Carbide tips. Brazed tips have not always bee sharpened!

2 ) The tool needs to be on the centreline of the work. Too high and it rubs rather than cutting. Too low and the Cross Slide is liable to jump forward when you are facing.

If you face the end of the bar and there is a pip in the middle, the tool is not on centre height. If it is too low, you can shim it up. The tin found in biscuit tins, and non corrugated food tins is usually about 0.010" thick.

It would be worth spending time to make a Centre Height Gauge.

Once you have brought the tool to centre height, you then adjust the Centre Height Gauge to that setting and keep it there for use in the future, to set other tools..

3 ) You really need another stage of reduction in the geartrain, (An extra stud, plus a small gear compounded with the one driven by the mandrels, to drive another large gear on the Leadscrew. Pair up the smallest with the largest in each case ) so that the Saddle feeds forward more slowly compared to the chuck. If you know, or can measure the pitch of the Leadscrew, you may be able to calculate the feed per rev. It would be good if you can get it below 0.005"/rev.

Don't know what Change wheels you have, but as an example, try something like: Mandrel 20 First Stud :60/20 Second stud 65/20 Leadscrew 55.. This shows the general principle. You might need to operate the Tumbler Reverse, while the lathe is staionary, to make the Saddle travel towards the Chuck again.

If it is not possible to slow the feed, try feeding by hand. You should be able to feed slower than a one stage reduction! With a ball handle rather than a handwheel, this will not be easy. But it will be good practice for you!

4 ) Your material is not ideal, as already been pointed out. Try to find some free cutting mild steel on which to practice. That should eliminate one source of problems.

HTH

Howard

OK have sent a PM andrew. I tried again with the EN3B and my C carbide insert and got a fairly nice finish flooding it with drilling and tapping fluid. However it still isnt flat, more ridged like it needs to slow down more. Does engaging the back gear slow the lead screw as well or not? Also do they do flat tools that arent at one point but cut sort of sideways? (sorry if im not making any sense).

Thanks

James

Hi James,

I think when folks suggest HSS tooling they most likely mean square (solid) HSS tools either ready made or as blanks.

Most of the likely suspects (Arc Euro, RDG, Chronos and so on) do them in sets of six in different sizes depending on what best suits your lathe – basically you need to know the height between the surface on which the tool will sit and the centre height. You can go smaller and use packing if you want… or buy HSS blanks and grind your own… or pick old industrial ones up on fleabay often for very little money (but pay attention to the tool size and postage cost).

I honestly dont know if HSS inserts are available for tooling that normally takes carbide. Possibly not.

Multigrade motor oil isn't really suitable as a cutting lubricant. It has all sorts of additives that mitigate against the cutting action that you're aiming for with a lathe.

As others have said, I wouldn't use the power feeds until you are really confident of the lathe's capabilities. Training lathes that used to be commonplace in apprentice workshop facilities never had any power feeds for that very reason.

Most of those tools will take CCMT 0602xx inserts (the xx is the corner radius) like these: lEAAOSw7P9bdDwP”>https://www.ebay.co.uk/itm/CCMT-060204-P20-30-Indexable-Carbide-Inserts-For-Machining-Turning-Steel/183380732175?hash=item2ab257e90f:glEAAOSw7P9bdDwP

Never seen HSS versions.