|Keith Charters||17/11/2020 14:46:10|
|5 forum posts|
Hi all, I am a relative newcomer to model engineering. I recently purchased a Warco WM250V lathe and Warco stand that is around a year old. I have now installed it in my workshop, which is a wooden shed. I have levelled the stand as best I can and have followed some of the tips found on this forum re checking the headstock alignment with the bed of the lathe.
I set up a 25mm bar in the 3 jaw chuck so that it extend around 180mm from the jaws and not supported by a centre. The bar is firmly supported by the chuck and there is no noticeable flex in the bar. I turned the centre of the bar down by around 2mm and left about 30mm at the chuck end and 30mm at the other end unturned. I then turned the two ends taking very fine cuts at the same crosslide settings and then measured these two ends with a micrometer. The end furthest from the chuck measured 24.65mm and the end closest to the check measured 24.87mm, so a difference of 0.22mm over a distance of around 150mm.
I am unsure if a twisted lathe bed would produce a taper of that magnitude or if there is misalignment of the headstock with the lathe bed.
Can anyone give me any advice on how to proceed and correctly level the lathe and remove any twist in the bed or if I need to re-align the headstock with the bed (a bit of a daunting prospect as I would need to strip the lathe down!)? How do I identify where I would need to add shims to remove any twist?
I am a little concerned that the stand and lathe are sitting on a wooden floor so I am give serious consideration to buying a suitably sized 30mm granite slab to sit the lathe and stand on and add some rigidity and also adding some levelling feet to the stand.
Any and all advice and suggestionsgreatly appreciated.
|1321 forum posts|
Congratulations with your new lathe. I got less difference between chuck and tailstock end when I tested my 290 lathe the same way as you did. My lathe sits on a steel stand on a concrete floor. I assume you have already found Harold Hall's pages on Setting up a lathe, if not there is good advice to be found.
|Martin Connelly||17/11/2020 15:23:24|
1602 forum posts
There are a few things that can cause this type of error, not just twisted lathe bed setups. The reality is that the bar is not infinitely stiff so some flex will occur. If your tool is not really sharp then at the tailstock end of the bar it might lift slightly due to the forces on it. This would cause a slight taper increasing away from the chuck. If the spindle bearings in the headstock have some play in them then the same thing can happen. What cutting tool are you using? What material is the test bar made out of? How have you set the tool to the correct cutting height? How sharp is the cutting tool? All these things have a bearing on the test that is being carried out.
|old mart||17/11/2020 15:23:36|
|2465 forum posts|
Having a lever type indicator with a magnetic base is very useful for checking alignments. When you took the finishing cuts at both ends of the bar, did you cut in the same direction each time? It would be normal for the end furthest from the chuck to be slightly bigger, but more than 0.1mm is cause for concern. I would check the spindle bearings first, that definately requires an indicator.
Edited By old mart on 17/11/2020 15:29:01
|Clive Brown 1||17/11/2020 16:16:29|
|580 forum posts|
The lathe cuts smaller at the tailstock end. My money would be on twisting of the bed as the cause unless the whole headstock is out of true, which seems unlikely.
To adjust the bed alignment, shims need to be added under the rear foot at the tailstock end or the front foot at the headstock end. I'd try that, a little at a time. Presumably the WM250 doesn't have adjustable screw feet built in.
A wooden shed floor isn't the ideal for maintaining alignment though.
Edited By Clive Brown 1 on 17/11/2020 16:18:51
|284 forum posts||
|Howard Lewis||17/11/2020 16:34:12|
|4095 forum posts|
Hi and Welcome!
A twisted lathe bed will cause work to be turned with a taper.
There are a variety of ways in which you can check for twist.
Lacking a sensitive level, it is probably best to use the method advocated by Myford.
This is set out in Ian Bradley's book "The Amateur's Workshop" on pages 27 and 28, or on pages 42 and 43 of "The Myford 7 Series Manual", by the same author. Basically, you turn a dumbell at least 6" long overall,.with a reduced diameter centre portion, and then take a light cut ( 0.002" - 0.004"  off the two full size ends. The two sizes are then compared.
The 7 Series Manual advises putting packing under the feet, at the Tailstock end. If the collar at the outer end is larger than that near the chuck, the the FRONT foot needs to be shimmed higher. If the collar is smaller, the shims should be placed under the back foot.
Biscuit tins are often made from tinned steel which is 0.010" thick. The shims should not be made of any material which is compressible. For the final very fine adjustments, sometimes SLIGHTLY increasing, or reducing the toque on a fixing can suffice., but the fasteners should all be reasonably tight.
When the two diameters are the same, the bed is no longer twisted.
If it needs to be said, the tool should be set so that the cutting edge is at centre height, and leaves no "pip" in the centre of the workpiece.
To check Tailstock alignment, a bar which has been accurately centred, and centre drilled should be held between centres, and a DTI, set at centre height (Either on a holder in the toolpost, with the Top Slide locked, and after Zero setting, the Cross Slide. or on a Magnetic base - to prevent any movement )
A three jaw chuck is not suitable for centre drilling to make an alignment bar. For this you really need a four jaw so that the bar can be clocked to centre it before centre drillinbg It is then reversed, end for end, re clocked again before being centre drilled. Silver Steel is more likely to be straight and parallel than ordinary bright mild steel bar
Once the bar has been centred at both ends, it is held between centres, and clock set to Zero (At centre height ) before being traversed to the Tailstock end. The tailstock should then be adjusted to halve the reading.
The clock is then returned to the Headstock end and reset to Zero, before being moved to the Tailstock end again.
Repeat adjusting to halve the reading until there is no difference between readings at each end. The test bar should not be rotated whilst these checks are being made.
The Tailstock is now aligned and turning between centres should produce work without a taper.
When turning between centres, to avoid damage to the Tailstock dead centre, the centre drilling should be filled with grease..
Once these checks and adjustments have been made, it might be worth making a Centre Height Gauge. This will save time in setting tools to centre height.
|1321 forum posts|
In Lathework (Workshop Practice #34) Chapter 3 he writes about getting the lathe to turn parallel and in Chapter 4 about a between centres test bar. The link in my previous post refers to his website.
|old mart||17/11/2020 18:11:00|
|2465 forum posts|
The Atlas 12 x 24 lathe that the museum inherited sits on a welded steel table with a drip tray. We put a large block of aluminium under the headstock, about 35mm thick and that allowed room under the tail end for adjustable bolts rather than shims. The Atlas manual says to use a sensitive spirit level across both ends of the bed to get them matching with no twist, I'm not sure if my Moore & Wright level is sensitive enough, but the "leveling" should be easier when the lathe is up and running. Some shim stock would be easy to get hold of, even cutting up an aluminium beer can would provide a usable source of material.
|Howard Lewis||17/11/2020 18:33:41|
|4095 forum posts|
Another way of levelling a lathe to take twist out of the bed, is to use raising blocks. Myfords advocate this method
Two pieces of box section, (To go under Headstock and Tailstock ) and four studs with lots of nuts should do the job.
The studs can pass right through the bench, with two nuts inside the box section, another on top, and two more (one each side of the lathe mounting foot.
The lower nuts around the box section are all tightened and then the upper ones, each side of the mounting feet are carefully adjusted to remove twist from the lathe.
This also gives more room to clear swarf from under the bed of the machine
|Keith Charters||18/11/2020 14:09:47|
|5 forum posts|
Thanks to everyone who responded lots of useful information there, especially in Harold Halls article. I have one more question. A number of people have suggested raising blocks as a method of removing any twist in the lathe bed. However, the Warco WM250V has three mounting points, 2 at the headstock and one at the tailstock. These are all in line parallel to the lath bed. So although they could be used to level the lathe along its length, they can't be used to level the lathe front to back. That would mean resorting to shimming, probably at the tailstock end. Does anyoine have any other ideas how I could achieve this?
Thanks to all. Keith.
|Dave Halford||18/11/2020 14:14:24|
|1127 forum posts|
Try not bolting down the tail stock and see what happens.
|Howard Lewis||18/11/2020 14:27:26|
|4095 forum posts|
If a check does show the bed to be twisted, (Hopefully, a three point mounting will avoid this ) the Headstock end will need to be shimmed in an attempt to rectify the problem.
1) Does a test piece give indication of the bed being twisted?
If "NO", end of discussion.
If "YES", then see what effect shimming has, using the Myford method as a guide, but probably in a mirror image fashion.
|Terry Kirkup||03/12/2020 15:11:41|
78 forum posts
Hiya Keith, fellow newbie here (I think I always will be).
This is what I used when I got my 290V. This is a very straight 20mm tool steel bar almost 30-odd inches long from a scrapped rolling machine. Trueness (is that a word?) looked pretty good to me as it was, using the dial gauge as shown. Pre-delivery had I dug two holes under the floor of my shed 18" square and 18" deep into clay then filled them with concrete, levelling as best I could with a 4' spirit level between them. After running the check above I removed the 3MT dead centre and brought the tailstock left until the bar just entered the taper, then ran the lathe. I could see no discernable runout at all between the end of the bar and the taper - a completely consistent gap while spinning, so more than satisfied, but maybe I just got lucky. The lathe itself need not be level as others have said, so you can ignore the horizon, but its constituent parts should be true to each other.
5031 forum posts
Try it again with the bar sticking out only 100mm. You will get a fair bit of flex on bar sticking out that far (180mm). If you can get a good reading over 100mm of less than say 0.02 or 0.03 mm taper you are good to go.
Use a razor sharp honed HSS tool for your test cuts. Carbide does not like those kind of small cuts and can spring the end of the bar away from the tool instead of cutting.
Edited By Hopper on 04/12/2020 07:01:13
5031 forum posts
Not sure what you are measuring there. If you are rotating the chuck to get your reading, all it's telling you is either chuck jaw run out or bend in that long, thin bar. If you are racking the carriage from left to right all its telling you is the vertical alignment of the bar relative to the lathe bed, if the chuck is holding perfectly perfectly true and if the bar is not sagging, which it will by by a certain amount. Doesn't really tell you if the lathe bed is set correctly.
If you want to check the lathe set up, try the turning test outlined in the first post but shortened to 100mm as discussed above in previous post. And read through the linked Harold Hall and Myford user manual pages on setting up a lathe.
|Howard Lewis||04/12/2020 10:03:49|
|4095 forum posts|
Are you totally confident of your 3 jaw chuck?
There are several parts within it that have to have clearance that allow them to move, plus, the jaws may not be ABSOLUTELY aligned.
Better to check using a Morse taper bar in the Headstock, that should eliminate errors in the chuck. You only need to worry about any inaccuracy between the male and female tapers and the parallel section of the bar.
It is taken as read that the clock is kept on the centreline of the bar.
Lacking a MT alignment bar, you could repeat the test, using a 4 jaw, where the work has been clocked to run true at the chuck end. But be aware that checking at the Tailstock end might reveal inaccuracies in the 4 jaw as well!
When you are convinced that there is no movement between bar and chuck, or flexing of the bar, then start experimenting with shimming the mounting feet.
To cast another stone into the pond, despite the advice to adjust at the Tailstock end, on my lathe, (larger than most on here ) The biggest effect was obtained by adjusting immediately under the chuck!
|Paul M||04/12/2020 11:24:09|
|46 forum posts|
I have the same Warco 250V lathe that I purchased new a couple of years ago. Mine is on the stand purchased for the lathe and sits on a concrete floor. I made extensions with adjustable feet for the outside of each end of the stand to widen the footprint and give some adjustment to level the stand and lathe.
In my experience, it is easy enough to level the lathe using the adjustable feet. The problem lies with the design of the lathe, having the headstock and tailstock fixing bolts in line. I have shimmed the tailstock end to try and reduce any twist (which is time consuming) and have got to what I think is the best I can expect for such a lathe.
For most of my turning I am happy with a slight error and have worked out ways to compensate when necessary. Most of my turning is generally within 100mm of the chuck resulting in errors that are within tolerance for most model engineering jobs. Where I need to work with longer lengths between centres or chuck and centre, I generally reduce any errors in diameter by adjusting the tailstock.
I think you have to accept that a Chinese lathe is not going to be super rigid and spending hours adjusting and sorting out a problem one day may return the next. Also don't lean on the lathe when using it.
|Steve Neighbour||04/12/2020 11:49:11|
|74 forum posts|
I also have a Warco WM250V and find it to be a lot better than most of the "British is best" camp would have anyone believe.
Mine is certainly a lot more rigid and accurate than I was expecting, so from my perspective the "poor Chinese quality" statement is completely unfounded, certainly for new machines.
Maybe I was lucky
Edited By Steve Neighbour on 04/12/2020 11:50:03
|Keith Charters||04/12/2020 12:16:02|
|5 forum posts|
Thanks again for all of your tips and suggestions, all very useful. I finally, after a fair amount of sweat and tears, managed to shim the rear of the tailstock end of the lathe, which has removed most of the twist. Harold Hall suggests aiming for no more than 0.002mm over a length of 100mm. I got mine to 0.005mm over 150mm, so pretty close to Harold's sugested figure and I do not think I can do much better than that. I may have to revisit this from time to time anyway, as my lathe and stand sit on a wooden shed floor, so there is likely toi be some flex in that over time.
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