Lathe cutting a taper

[bernard towersParticipant @bernardtowers37738]

I take you back to the first half a dozen posts!!!!

[Chris MateParticipant @chrismate31303]

OK, I can see the problem with this lathe with the wiggler applied.

 

This lathe bed is such that the Tailstock follows a “Different Track” on same bed than the Crosslide. A lot of lathes are similar but not all.

-Tailstock=Wiggler illustrate no visual difference with Tailstock moved to rear of bed.
-Crosslide=Wiggler illustrate visible a difference Crosslide moved to the rear of bed, now this is a problem.
-This means the headstock points down visually a bit over lenght of bed regarding crosslide track……..

Conclusion=I can see a problem by using the wiggler, which means I dont know yet how to fix it easily.

Maybe I can twist the bed to satisfy this test, see if it repeats at chosen distances as I move the crosslide towards heastock/chuck.  If I can twist bed such that it dont deliver a wave of ups & downs, it could be a selution for this track, then adjust the Tailstock as required if possible.
-Or I can just live with it as I did so far…….
-It puzzels me a bit how the two tracks can lead to this type of a difference on one, I doubt it can be wear.

[Tony Pratt 1Participant @tonypratt1]

Chris Mate,

I would seriously suggest you read carefully the previous posts and perhaps research the conventional method for setting up a lathe to cut parallel on the internet. You are going off at a tangent and trying to reinvent the wheel with confusing results.

Tony

[PeteParticipant @pete41194]

Tony is 100% correct.

But I’m completely lost by your use of a wiggler Chris unless your somehow using the incorrect description. I honestly can’t see how a wiggler would show anything useful at all.

Most lathes will have two V and two flat ways, the carriage will generally use the V way closest to the operator, and the flat way at the back of the lathe bed. The tail stock will probably use the V way at the rear of the bed and the flat way closest to the operator. That’s just about standard practice for lathe manufacturers, although there are exceptions like a Myford that use flat ways.

And you really can’t do any of this without at least a dial test indicator (dti) and a plunge type dial indicator. Plus the magnetic bases to set them up and use them.

Dial test indicator https://www.amazon.ca/Indicator-Precision-0-0005-Measuring-0-0-8mm/dp/B08JQG17FQ as an example of what I mean.

Dial indicator https://www.humboldtmfg.com/dial-gauges-counter-clockwise-rotation.html

Those can be in either Imperial or metric measurements. I’d want the dial indicator capable of displaying at least .001″ / .02 mm and the dti capable of .0001″ / .002 mm. These are just part of the basic needs for anyone owning machine tools and they will be used often. Added to that, a 0-1″ / 0-25 mm micrometer. But with the size of lathe you have, I’d probably add a second 1″-2″ / 25-50 mm micrometer as well. For what your trying to do, any caliper including digital simply isn’t accurate enough because there mechanical design can’t provide the same level of accuracy and repeatability that a micrometer can.

 

[BazyleParticipant @bazyle]

I think what you are saying is that the bed is worn close to the headstock such that the whole saddle/cross-slide dips down towards the headstock. Yes a wiggler can be used to show this. This is common for well used V-ways. The only solution is a full bed regrind which has other problems too. However the good thing is that it is not that serious for most turning. If the tool is set at dead on centre height it will only make a noticeable difference on longer cuts, which are not so common. You can halve the effect if you set the tool a tad lower (thou) at the headstock. Also if the key features of the part are at each end you can compensate.

It is likely that the wear is only at the end, with most of the bed true. So some things can be turned at the good end. Eg if you need a 6 in axle to be true all along make it at the far end using a 12in bar before cutting to length.

[PeteParticipant @pete41194]

Except the OP’s first post says this. “I bought a new CQ6133 lathe few years back. I worked around the taper cuttng problem, but are back at it again”. A lathe that’s a few years old is already worn that badly? Very doubtful.

[BazyleParticipant @bazyle]

Well I can’t remember what I had for lunch yesterday let alone what was in a post days ago. It is odd that the saddle dips and not the tailstock so it will be interesting to hear what happens if twisting the bed corrects the saddle.

[Tony Pratt 1Participant @tonypratt1]

Hi Chris,

How about some pictures of your set up?

Thanks

Tony

[Howard LewisParticipant @howardlewis46836]

A new lathe is unlikely to be worn, can only repeat the advice to remove any twist from the bed, before doing anything else.

The method of checking and correct twist is outlined in Ian Bradley’s “The Amateur’s Workshop” and in his “Myford 7 Series Manual”, otherwise known as “Rollie’s Dad’s method”

The good thing is that Ian Bradley says bolt down the Headstock and then tells where to shim or adjust at the Tailstock end.

If the lathe is on some form of raising blocks, the screw adjustment allows more precise adjustment than using shims.

Once the bed is free from twist, then you can buy or make (Easy if you have a four jaw independent chuck, a magnetic base and a clock that reads to 0.0001″) an Alignment bar and align the Tailstock.

With a new machine, little else ought to be needed

Howard

[Chris MateParticipant @chrismate31303]

Howard, I understand what you saying. I feel I may have a problem before I can attend to that, and the problem is if I put a bar in chuck, I can easily move it up to .2mm with one finger at 110mm stickout, with the HSS bar not flexable with one finger, its not the chuck. I noticed I cannot adjust the bearings more, I dont want to overtighten anything. I do understand that the taper roller bearings fitment is not similar to that of a car. I did start getting problems with a insert cutoff blade trying to part……I feel if its somehow bearing related, it will keep on messing with the shimming, like next morning I get different readings…….Something other than the headstock/bed is messing me around…..

I am back at rechecking the spindle & bearings….I can get new bearings locally, no problem. Like mill I want to replace bearings with Timken type, it transformed the feel of the mill, the mill quil was definately easier than this looks to be. I spend a day on it before making decission finally.

It may take a while…….

[Keith LongParticipant @keithlong89920]

Chris – if the chuck mounts to the lathe spindle or to a backplate with bolts, check that those bolts are tight and not allowing the chuck to move slightly.

Some years ago I helped someone diagnose similar problems on a lathe and that’s what we found. The bolts appeared to be tight but were JUST loose enough to allow the chuck to move very slightly, the register had a small amount of clearance as well.

Keith

[PeteParticipant @pete41194]

Like anything else, the proper analysis of issues with machine tools is mostly a process of elimination. Or verifying what’s known to be correct versus what isn’t. Spindle bearings and especially the tapered roller type have pretty tight limits for measurements when there set correctly or they aren’t. Anyone with a dial indicator ought to be able to 100% and easily verify both the axial and radial clearances on there own lathe in less than 10 minutes. Without those measurements and some known numbers, its just guessing for what the problem might be.

[Howard LewisParticipant @howardlewis46836]

FWIW, get the lathe properly set up, and then if there is a problem start worrying about wear or slackness.

Your machine is a hobby lathe, and virtually unused, so unworn.  It did nor cost anything like as much as an industrial toolroom lathe.  So don’t expect the same level of precision from it.

Thousands of hobbyists are quite happy with the performance of their lathe, “out of the box”

Be realistic, and don’t expect a three jaw chuck to hold work concentric to much better than 0.003″ (0.075 mm)

We do not work in temperature and humidity controlled Standards or Calibration rooms, so our measurements are not REALLY accurate.

So no delusions absolute accuracy!

If you are tugging on a bar sticking out of the chuck, you are not reproducing the conditions under which the machine actually works. Once the machine is rotating, temperature and oil films will affect behaviour. Precision grinders are run for some time to warm up before starting work for real, for this very reason.

Get it set up properly, first of all.

Set it up as Ian Bradley advises in “The Amateur’s Workshop”, and “The Myford 7 Series Manual” (“Rollie’s Dad’s Method”) to remove twist from the bed.

Don’t try to run and complain that your shoes fall off, if you haven’t tied your shoe laces!

Then fit the 4 jaw and make an alignment bar. You will get useful practice clocking the test bar (Preferably precision ground, or silver steel) until it is concentric.

The accuracy with which you do this will determine the accuracy of your Alignment bar.

Then you can check, and if necessary, adjust the alignment of your Tailstock.

Once you have carried out the basics, you may be surprised at how well the machine performs!

Howard

 

 

[bernard towersParticipant @bernardtowers37738]

Howard, everything you say is true and been said before on this post but its falling on deaf ears, save your time and and get in the workshop.

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