|James Smith 21||05/07/2020 00:29:13|
|2 forum posts|
(new to the forum and to turning so sorry in advance)
I have a britannia lathe which i recently aquired for the reasonable price of £350 with 3 and 4 jaw chuck and drill chuck but i need some help. It has a poor surface finish which i think is due to the leadscrew going too fast, however i cant slow it down any more i dont think. This is the change gears setup. This and this are pictures of the lathe, though im not using that HSS tool, im using some carbide tooling i got on ebay, china's finest! The surface finish looks like what i would call tearout in wood. It also looks like the grooves are resebling threads, like in this picture (not my part but shows the finish i am getting quite well)
Any help is appreciated,
4649 forum posts
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.
|Andy Carlson||05/07/2020 09:33:27|
|258 forum posts|
I'd suggest avoiding the power feed and carbide for the time being. If you don't already have one, get hold of a bench grinder and (important!!) a set of protective goggles and learn to sharpen and grind HSS tools. The usual grey grit wheels that come with most grinders can be used on HSS. There are plenty of resources online such as...
You will learn a lot more from driving the lathe by hand and you will get feedback via the resistance of the handwheels to help you understand whether the cut is going well or you are asking too much. I don't think any amount of reading or advice from others can be a substitute for this.
If your lathe has locks on the slides that you are not using then lock those slides while you make your cut - it will rule out those variables from any finish problems.
An old lathe will likely have some play in various places, for example on the cross slide feed but there are things you can do to help. When setting up for a cut you should always approach your intended setting from the same direction. If you accidentally wind a bit too far then you need back the wheel off a good deal (maybe a whole turn) and then approach again from the original direction. This ensures that you are always on the same side of the play.
Take things slowly and carefully and keep yourself safe. Enjoy your lathe.
5290 forum posts
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.
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
|5924 forum posts|
+1 to Hopper's "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."
I'd eliminate the duff material and carbide as possibilities first, not least because my last bit of turning produced almost the same spiral torn finish.
I was running a vibration test, not making anything, and ran a big blunt carbide cutter at slow rpm down a length of scrap mild-steel pipe at fine feed speed. The result is a poor cut like yours.
Not unexpected in my case!
I can get a good finish on my nasty steel pipe from the same carbide insert simply by doubling the rpm, feed-rate and depth of cut. Probably not an option on a Britannia, nor is high-power machining how I like to work! A nice sharp HSS or carbide insert might well fix the problem.
If a sharp cutter fails to get a reasonable finish on EN1a-Pb after investigating various rpm and depths of cut, time to look at Hopper's other suggestions. I'd start with easy problems like adjusting loose gibs, but don't be disheartened by inconsistent results because an old lathe might be worn in several places. Take it step by step. The forum is helpful, especially if you can provide photos.
Maybe the banjo gear ratio could be improved, though it looks reasonable to me (any Britannia owners about?)
|James Smith 21||05/07/2020 12:47:37|
|2 forum posts|
Ok let me clear some things up. I have done some wood turning but it was all with my father's late and chisels, I doubt he would be happy if I strapped one to my lathe! I am trying to turn EN3B from metals4u. The insert is Chinese yes, it's a 10mm tool, anybody know where I could get inserts for it? I did try hss with a single point tool but it still left that same finish. There is a bit of play in the cross slide, but I had the tail stock in and the cross slide always going the same direction, not winding it back. Headstock is tight as, I checked when I bought the machine. I think a worn chuck would be on the cards, I tried to turn something about 3 inches from the chuck without taiostock and it just wanted to ride up on the tool. The chuck was tightened down as much as I could and I had tapped it onto true with a dial guage and spanner!
|pgk pgk||05/07/2020 13:00:18|
|1846 forum posts|
The chuck may be worn but if it's gripping the material it's gripping the material. You can test how much slop you have in the headstock system by sticking a length of decent diameter rod in the chuck and seeing how much it moves about.
Beyond the wise words from the guys above I'd add that you should have a go with a decent diameter material - say 1inch+ and have no more than 3x the diameter sticking out without tailstock support... better only an inch or so for a test with HSS tool that has the correct profile and has been honed and is correctly on centre. Carbide always wants more depth of cut (pressure) against the work than HSS so you're more likely to push the work away if there's any slop.
|Paul Kemp||05/07/2020 13:04:12|
|514 forum posts|
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.
|Andrew Entwistle||05/07/2020 14:23:14|
78 forum posts
Hi James, I have the same 1930s 4" Britannia with taper roller bearing headstock. On mine the spindle wall around the MT2 taper is quite thin and I have found that for diameters above about half an inch the spindle is just not rigid enough to get a good finish, unless using razor sharp HSS or xxGT carbide inserts designed for alumumium and stainless. With the right tool, feed and speed it can do anything, in backgear it has happily made its own chuck backplates up to 6" diameter.
Edited By Andrew Entwistle on 05/07/2020 14:24:05
|5924 forum posts|
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.
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:
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.
Edited By SillyOldDuffer on 05/07/2020 14:59:20
|James Smith 22||05/07/2020 15:11:27|
|3 forum posts|
OK, had to make a new account to reply as my email is playing up, hopefully that will be resolved soon. I've been using 15w 40 as a lubricant putting it on with an oil pot thingy. Andrew I will try to send you a PM if that exists on this forum to ask you if you have thread cutting tables for the lathe, as I do not have anything.
|Howard Lewis||05/07/2020 15:58:34|
|3375 forum posts|
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.
|Andrew Entwistle||05/07/2020 19:18:36|
78 forum posts
James, please do PM me, I can send you a spreadsheet of changewheel configurations I have used, and a program that will calculate the combination for you.
|James Smith 22||05/07/2020 21:11:03|
|3 forum posts|
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).
|James Smith 22||05/07/2020 21:12:47|
|3 forum posts|
Also does anybody know where i can buy replacement carbide tips for my insert tools? Dave said earlier to use HSS, can you get HSS inserts?
|Andy Carlson||06/07/2020 00:11:13|
|258 forum posts|
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.
|Andy Carlson||06/07/2020 00:19:39|
|258 forum posts|
One other thought - small (1/4 inch??) HSS tools can be used on bigger lathes by putting them in tool holders. The holders are usually slightly angled to the left or right for different turning jobs. Not quite 'inserts' but a similar idea. To show what I mean, this eBay lot has two at the top of the photo...
Not sure if many people use these nowadays.
52 forum posts
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.
|1749 forum posts|
I seem to recall that HSS thread-cutting inserts are available.
52 forum posts
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.
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