My feeling is gap piece maybe set wrong It’s hard as if I was in front of the lathe I could track and measure wear and reset tool path.
A square head Colchester. The headstock register doesn’t have the bed vees continuing through like a roundy
Where's the cross-slide though. I have a 2500 and I find it hard to tell them from a triumph at a distance. So it's got me intruiged..l
Get someone with a good idea of machine setup to take a look at it. You could have a twist in the bed. youd be better using a good grade of machinable steel. Trying to take a really light cut on a softer material that could push away from the tool pressure will lead to odd results. Have you got a MT test bar? If you put a test bar in the taper in the headstock you’d be able to measure 1.5 thou of deviation easily with a clock running the carriage back and forth.
Some twist at that rate? I'm more with the gap is set wrong - they aren't pinned, just set and tightened down.
They’ve not got the best made cabinets/sub structure to them. .0015” isn’t hard to induce on an aluminium bar. I could probably encourage that kind of movement with a hairdryer. Even if the gap bed is sitting high, a misalignment in the vertical plane would not change the cut by 1.5 thou. if the gap bed is at an angle to the ways then perhaps but on a triumph the carriage will only be a little on the gap bed piece, the bulk of the carriage must still be on the main ways.
The gap piece isn't in great. The main 2 hold down screws had stripped threads so someone in the past bored them larger and re tapped the threads. They are a tight fit in the gap piece so no slack to move them around. I will either have to open up the holes a bit or reduce the bolt diameter a tad. Having said that I extended the topslide so only 2" of the 6" was cut on the gap.
Yes but not the cause of this problem as I get a taper before I reach the gap. Definitely needs sorting though!
Small horizontal screws behind the gear train and the headstock pivots on right rear corner. I set mine by the two collars method. Don't turn the full bar to diameter. Have a relieved section in the middle and just concentrate on getting the same dimension over two points, one near chuck and one about 6" away.
I did a little digging around with machine setup some time ago, as I recall it is a non trivial process! For such a simple alignment issue, it can be fantastically complex where one error can be dialled out or hidden by another. Another way to approach the problem is to establish where the error is not. The bed can twist, bend and yaw and be worn and of course it might not even be an issue with the bed. It would also be very easy to really mess things up if you start going after factory set alignment, especially if you adjust that to inadvertently dial out an error elsewhere. I think my first port of call would be to a company that specialise in configuring machines. Even if it cost a few hundred quid, that might work out cheaper in the long run.
Not too difficult if following the right procedures in the right order. 1) Precision level across the ways first to eliminate twist. 2) Tailstock alignment to bring on centre. 3) Headstock alignment last of all. Possibly repeat 2 and three if headstock way out initially.
I have a Triumph and have the same problem, The banjo has to come off. It helps to have a short arm Allen wrench to get to the left side Allen bolt, looking to the front from the back. The adjustment is tedious on Mine as the headstock moves slightly when finally torqued down. I have had the adjustment block apart for cleaning as it was covered in chips. The pins that the adjustment screws seem to be too soft and indent when taking a cut and it needs adjusting again. The adjusting screws are socket set screws with a ground taper on them. The pins seem to be soft steel which might not be up to the job. Thinking to remake Them with something a little harder.
Google “Rollie’s Dads Method” , a classic way of aligning a lathe. https://www.google.com/url?sa=t&sou...lignment.pdf&usg=AOvVaw2ef7quFql8vWjaDrzjtqgy
It shouldn't matter that the adjustment pins are soft they are only used to align the loose headstock which should be full tightened down again after each adjustment. I seem to remember one of the hold down bolts being a particular pain to get too so left that loose until final alignment complete. The adjustment bolts were awkward but not too bad. That was on a round head student.
Once the head stock was adjusted and turning straight, the problem slowly came back. I took the adjustment block apart and noticed the indents on both pins. I put the pins back on a new section of pin, adjusted it again and the problem slowly came back again. I ill have to wait till the middle of winter when things slow down and look for 2 sets of indents. If found I will make a set out of 01 tool steel and harden them.
Is it a continuous taper, that would suggest alignment If its localised to an area then your bed is worn
The adjustment block is just to help you move the headstock into precisely the correct position with the hold done bolts JUST nipped up. Once aligned the hold down bolts should be properly torqued down and the adjusters could be slackened off, as at this point they are no longer doing the holding. I’m not at all surprised that there are dents in the pins as the headstock is a beefy lump for a small screw to move even when the hold downs are fully loosened, but the dents have no relevance if you have properly tightened the hold downs once adjusted.
My advice from thirty years of being machine rebuilder. Level bed for twist Remove suspect gap piece and clean all faces. Seating accuracy can be affected by corrosion and being refitted on a machine with twisted bed. Align gap with dti preferably with clock on fixture running on tailstock ways if still good Check headstock to toolpath using test bar( I have one you can borrow) Check headstock to tailstock ways which should have less wear as you want headstock aligned not cockled to a worn bed Minor adjustments to headstock if necessary Set tailstock to mandrel test bar and perform between centres machining test but accept it’s a elderly machine and hand finishing will be necessary occasionally Ignore what I’ve said and listen to shed tinkerer or a youtuber
