Just Tooling Around

[Ian S C]

From what I see, I would say the work is being deflected by the tool, I would use a much smaller radius on the tip of the tool, and slow the feed rate.  As the speed will be about as fast as the lathe likes to run, the feed should not be too tediously slow, try hand feeding.  Ian S C

[arnoldb]

I'd differ from Ian S C; if you got taper due to deflection, the narrow part will be closest to the chuck, rather than away from it.

Were you perhaps feeding with the top slide rather than with the apron ? - If you did, your top slide is not parallel to the lathe bed.  Don't trust the graduation marks on the top slide for accuracy.

As a suggestion: your top slide is nearly half-way off it's dovetails.  This is not ideal, as you're losing a lot of rigidity there.
Screw the topslide fully onto it's dovetails, and try the cut again, hand-feeding with the apron.

Kind regards, Arnold

[tel]

In a word, yes! Wot Arnold said.

[steamer]

YUP!

Dave

[Don1966]

I had trouble with my Micro Mark which is the same lathe is your grizzly. Another problem I had was the carriage adjustment was to loose. This gives you side to side Movement and can give you a taper. These slides are hard to adjust read the manual carefully on how to adjust it.

Don

[Rayanth]

yes, I was feeding with the top slide (noted earlier in that wall of text I wrote on saturday) ... It's that far back because I'd had issues with it binding when getting towards the end of the screw, but nowhere else in its run... the binding was causing a little bit of twist, which was giving me wavy cuts, so I pulled it back more. I had torn it apart to re-clean it, but I'll be doing that again anyway when I get the DRO's later this week.

The top slide is, as far as I can tell with a machinist's square, nearly perfectly parallel to the ways... I'll look for another way to confirm this when I put it back together.

Thanks for the input!! 

-- Rayanth

[smfr]

Sounds like this wasn't the problem, but you can always tell if you're getting a taper from deflection caused by the tool; if you do more passes without moving the tool, it will keep cutting on the outer end for a few passes.

Simon

[Rayanth]

arnold, you suggest feeding with the apron -- I would think that would be less ideal/accurate than feeding with the top slide?

regarding other comments - my cuts were very shallow, no more than .010 per pass, down to .002 on the final few passes, measuring with micrometer after each pass near the end to recalculate how far to go (i understand the doubling aspect, but still don't have a feel for it). All cuts at a new depth were made by starting at the tailstock end and working towards the chuck, then back out again at the same depth...on the return, very little was noticed in the way of new chips....mostly from making faster cuts before i got near the finishing cuts, which were done much slower.

I am suspecting my top slide is not quite perfect. my machinist's square is a bit small to be checking it with to any serious accuracy, but i haven't done the math to see what the angle must be, if i have .005 over .500 run.

So my plan is to mix the suggestions. Arnold suggests feeding with the apron...i tend to bash my knuckles with the cross-slide handle when doing so but I can see the wisdom in that it WILL tell me if i'm cutting straight there, which will confirm my top slide is angled if i get a straight cut. I don't quite have any sacrificial rod to turn a long length held between centers to see if i'm getting deflection...but I will take lighter cuts, and regrind that bit to a smaller radius (I had at first a smaller radius but did not get a decent cut with it, so i made it a hint larger and got a nice cut)

All of this will probably be done after I have the DRO's and QCTP later this week, so I will have a more accurate cutting tool height as well.

Will keep you all posted, and thanks again for the input! I have no way of getting anything like this in person

--Rayanth

[steamer]

Rayanth...

Feed with the apron....slowly..

Dave

[mklotz]

measuring with micrometer after each pass near the end to recalculate how far to go (i understand the doubling aspect, but still don't have a feel for it).

Measure how far you have to go, halve that and set the zero of the handwheel that amount off from zero.  Then, as you cut, you can see how far you have to go by looking at how close you are to zero on the handwheel.

I don't believe you (or anyone) can set the compound to zero accurately with a square.  I wouldn't even consider trying to do it.  Mount a DI to the compound and have it bear (at center height) against a good piece of ground shafting held in a collet.  Traverse the compound while adjusting until the DI shows no motion over the extent of the traverse.

Once aligned, forget the compound and use the carriage traverse to move the tool as Arnold et al have indicated.  The compound is there to use when turning short tapers - a fact we believe you've discovered.

[Rayanth]

Thanks marv, that helps clarify things a bit...and I knew that DI would come in handy somehow

Sadly, I only ordered DRO's for compound, not for my apron... I really just cannot trust the handwheels, knowing that they are off by .0004 for every thousandth. Even setting to 0, a cut of .050 is really only (by seat of the pants math) about .0492, doubled is .0984...when I intended for .100. I realize the differences are pretty small but knowing they are there bothers me greatly.

Guess I can use the DI against the back side of the carriage to see how far I'm moving when i use the apron wheel?

-- Rayanth

[tel]

The dials are only a rough guide at best, when you are getting close it's stop and start, measure, put on a tiny increment, go again .......

Oh, (chorus) and cut with the dammed APRON!

[zeeprogrammer]

Guess I can use the DI against the back side of the carriage to see how far I'm moving when i use the apron wheel?

That's what I do. Someday I'll have DROs.

[Rayanth]

The dials are only a rough guide at best, when you are getting close it's stop and start, measure, put on a tiny increment, go again .......

Oh, (chorus) and cut with the dammed APRON!

So...what you're saying is that I should cut with the apron? 

On second thought, I don't even wear an apron....

One day I'll figure it out 

--Rayanth

[mklotz]

Two inch DI's have been the poor-man's DRO on my mill drill since I bought it back in the 70's.

The Z-axis DI is fitted with a clever adjustable slider that moves the rod to the mid-extension location with a simple push.  Tighten a finger screw and I'm ready to measure +/- 1" up and down from any position.

The X-axis one pushes against a pad that is affixed to a sliding lockable rod.  Thus it can be set to any desired reading at any table position.  The Y-axis one is similar in operation but the mechanics differ slightly.

My old Unimat is now permanently configured as a high-speed miniature mill/drill.  It too has 2" DI's for the X and Y axes.  A 1" serves for Z since the quill throw is so tiny.

The lathe has a DI fitted on the front way on a sliding holder/stop.  A magnetic-based DI can be attached to the top of the tailstock to measure drilling depth.

Now that I've written this I realize just how many DI's I've got floating around the shop.  (There are several more I haven't mentioned in committed measurement modes as well as the ones  in the toolbox for taking to the job at hand.)