Myford ML7 Turning Between Centers

John.

 

So is the bar not parallel along its length - perhaps you could give some measurments of the diameter in various positions?

 

 

Martin.

 

Martin, The bar is parallel along it's length it is exactly the same diameter along it's entire length, but when I run the DTI down it using the carriage to do this it starts off at the tailstock end on zero and is 4 thou more at the Mandrel end but in all other respects the bar is spot on.

John

John

Get a 6"length of 1 1/4" free cutting mild steel, put it in the 4 jaw and set to run true. Take a light cut along it just enough to clean it up, for this I would recommend a H.S.S. tool, carbide tools do not like small cuts of a few thou. You can then see if the head stock is properly lined up with the bed. The size of the material is important as it will be less likley to deflect than say 3/4" dia. It is also important to make sure your headstock bearings are properly adjusted before you start this test. The other alternative is to try and lay your hands on a test bar and use that in the headstock morse taper. I would venture to sugest that the problem lies in wear in the bed/carriage. When turning, the carriage is driven by the half nuts, but when you are clocking I suspect that you are winding the carriage by use of the handwheel, if there is wear in the bed/carriage this could be causing the carriage to rack giving the reading on the clock that you have described.

John.

 

Assuming that you're clocking the bar from a similar position to that of the cutting tool, then I think there must be some error in the information you're posting, because it's not really possible to have a cutting tool move away from the bar (as implied by your 4 thou reading) and yet have that bar remain parallel.

 

If the DTI reading is consistant, I would be inclined to take another light cut along the bar (don't remove it from the lathe) and check with a micrometer for parallel again. If it still checks out OK, then I would do a test once more with the DTI to confirm the results and let us know what you find.

 

Is the lathe turning parallel with a shorter workpiece and no tailstock support?

 

 

 

Martin.

Hi all,

I agree with Martin that if the DTI and the tool are on the centre line it is not possible to have this difference. Think of it this way. If the tool is just touching the bar at the tailstock end by the time it reaches the headstock end it will be taking a 4 thou cut so the bar would now be tapered. It is being implied that when the tool is removed and replace by the DTI (With no other change.) the carriage follows a different path.

This topic started with a concentriciity problem. I do not think this is one problem but two unrelated ones.

 

Les.

If you move the x slide back to fit the DTI /Clock it may influence the stress on the sheers

zero x slide when turning and clock with X slide in the same place This is a puzzle !!!! The picture is a bit clearer now Or is it ? This may be the ( change) Les was looking for

Nobby

Les and Blowlamp, I think you have helped possibly solve this problem you have assumed that I have put the DTI in the Toolpost to run it down the workpiece ( obviously this is the way it should be done but remember I am a raw beginer trying to get things right). I put the DTI on it,s Magnetic stand on the crosslide in the position were the rear toolpost would fit and ran it down the center of the workpiece on the opposite side to the toolpost. I have taken the lathe off it's base and reinstalled and levelled it cut new test pieces to correctly level the lathe. With the test piece in the chuck ( there was another problem here the 3 jaw that came with the machine was not as accurate as it should have been and I now have used a Burnerd chuck which is fine) the toolpost end was in a dead center not live and yhe tailstock cut was 5 thou bigger than the mandrel end, lifting up the tailpost front mounting point sorted this, this means that the bed at the tailpost end is not plumb but it cuts true. I then cut the workpiece between centers and adjusted the tailpost to get a true cut.I then used the DTI in the manner I have described and there was mow a 2 thou difference although the test bar was parallel, I also noticed at this point that by gripping the crosslide I could effect a 2 thou difference in the DTI reading. I have had enough now for tonight and will continue tomorrow. What effect would using the DTI in the manner I have described have on the readings I obtained.

John

John

It appears from your post that you are aligning the tailstock by twisting the bed, this is wrong! The bed must be set up to be true in every direction. The tailstock should then be adjusted by means of the adjusting screws in its base. If you do not do it this way when you move the tailstock towards the headstock it will increasingly become out of line. It looks like you have used one error to cancel out another. From what you say it looks like the gibs on the machine may need slight adjustment, they are correct when you feel a slight resistance when the carriage/cross slide are pushed by hand (you will need to remove the cross slide screw and if possible the carriage handwheel) It is a fag doing this but the results can be worthwhile.

Dusty, This is not the case I have adjusted this Lathe in the correct order as in the instruction book as I have explained before, I have done this more than once, it looks like my Lathe was in correct adjustment and is now , it was my method of using the DTI that was the cause of my supposed problem, the crosslide has a small amount of play which I intend to remove and draw a line under this and get on with using this Lathe to make my Stuart Twin Launch engine. I will be posting further questions regarding obtaing a fine finish on the crankshaft in a new post. I am most grateful for all the help I have received to date from this Forum.

John

I am sorry to come to come in at such a late juncture but I have only just seen this posting.

 

Before getting too hung up on the error being highlighted by running a clock along the length of the test piece, I think we should take a step backwards: -

 

(1) How old is this ML7?

(2) What condition is it in? By this I mean the slideways, gib's, backlash etc etc

(3) What size is the test piece? Length and diameter

(4) What type of cutting tool is being used and what condition is it in?

(5) What difference is there in the diameter along the bar length?

(6) Assuming an original error of .004 along a 12" length, now reduced to .002 alomg the same length, what error are you expecting?

(7) The bed in the zone in front of the headstock is almost certainly worn significantly more than the tailstock end, has this been carefully checked?

 

Sorry to labour that little lot, and I guess given a few more minutes I could find another half a dozen imponderables, but it occurs to me that we need to establish the realistic level of accuracy that is expectec. Is it in fact beyond the remit of such an elderly machine?.........incidentally please don't be offended by that remark.

 

Finally and perhaps crucially, what sort of work is going to be produced on the machine in question, and to what tolerances? After all if there is to be a predominance of short components produced to diameters of plus or minus .004" then does it matter at all. If absolute precision is required then is this the right machine, or should secondary processes be used for finishing.....such as grinding?

 

HTH rather than hinders.