Lathe: checking for taper with new bed

[dml66]

I recently migrated my 7x10 HF mini lathe to a 16" bed using the LMS kit. Everything is running smoothly, including the Z-axis DRO scale which had to be lengthened.

The last step is to check for bed twist-induced taper and correct it, if needed.

I have a 24" long piece of 13/16" diameter aluminum round bar for testing, there's about 14" between the ER32 spindle collet chuck face and a live center point in the tailstock.

Is their wisdom in measuring cut taper over the full 14" or, is a smaller distance, say 7", sufficient to establish taper?

Thanks.

 

[VicHobbyGuy]

I'm interested in the sequence that should be followed. For me, it's one of those "I don't know where to start" sort of jobs.
How did you check the headstock and tailstock alignment to the bed- which I guess you have done already?

 

[dml66]

I'm interested in the sequence that should be followed. For me, it's one of those "I don't know where to start" sort of jobs.
How did you check the headstock and tailstock alignment to the bed- which I guess you have done already?

Good questions.

It's been so long since I had to sort out the 7x10 bed, I had to clear some cobwebs.

Once I figured out the 7x10 was turning a taper, I spent a great deal of time aligning the tailstock in an effort to correct the taper. What I recall finding is the amount of taper could be minimized, but not eliminated by adjusting the tailstock. I also fiddled with trying to adjust the headstock but there really isn't a way to do that from what I can tell; once the 3 bolts securing it to the bed are torqued down, the headstock position is predetermined. I went as far as ordering a replacement headstock, firmly believing it was the cause of the taper, that turned out not to be the case.

That's when I learned about bed twist, once I devised a way to untwist the bed, the taper disappeared.

So, I do need to see if the machine is turning a taper without regard for the tailstock, if it is then I need to address bed twist, if not then I need to make sure the tailstock is properly aligned. I'll probably start by turning a short 13/16" diameter piece, say 2" long, without the tailstock to see where I'm at.

 

[ShagDog]

Watching. Interested to see if taper is removable (with repeatability) on a mini lathe.

 

[VicHobbyGuy]

I also fiddled with trying to adjust the headstock but there really isn't a way to do that from what I can tell; once the 3 bolts securing it to the bed are torqued down, the headstock position is predetermined. I went as far as ordering a replacement headstock, firmly believing it was the cause of the taper, that turned out not to be the case.

Shimming the headstock seems to be the fix for some alignment problems. Ted Hansen and others have mentioned that in the Facebook 7x mini lathe group.

It's interesting that you had bed twist in your 7x10- had you bolted it down to the bench?

 

[GrifterGuru]

Ted Hansen, Great guy, great comms. Purchased his book "The complete Mini Lathe Workshop" (ISBN 13: 978-0-941653-48-0) directly from him as I could not locate a copy in the UK.

Chapter 8 "alignment Essentials", page 29, lower left starts with "Headstock Alignment" then moves onto Tailstock alignment.

Made contact with him through the 7x mini lathe group on FB, then, for some reason, without warning I got booted? No rhyme or reason, no notification, just went to look in to double check a post and could not find the group (which means I was banned). Wierd.

 

[dml66]

Shimming the headstock seems to be the fix for some alignment problems. Ted Hansen and others have mentioned that in the Facebook 7x mini lathe group.

It's interesting that you had bed twist in your 7x10- had you bolted it down to the bench?

The lathe was not bolted to the bench to start with, once I decided to see if the taper was bed twist related, I did bolt it to the bench in such a manner that I could use feeler gages to induce an opposing twist. It's a simple arrangement as shown in the picture; below the benchtop, the thru bolts thread into tapped flat bars which function like t-nuts.

 

[dml66]

Well, maybe I got lucky on this one .

6061 AL.

After a couple cleanup passes I made a 2" long, 0.003" DOC finish pass, the indicator shows an almost undetectable amount of taper. I'll make a few more turns for consistency but, for now, this one looks good to go. And yes, the indicator is live .

 

[GrifterGuru]

Try the collar test... One collar at the chuck end, one collar as far towards the tailstock as possible and see what the result is, but before you do that though, use a test bar to check tailstock alignment

 

[ddickey]

Check taper by measuring with a mike.