Hello:

After a long hiatus while waiting for some tools from Asia, I started working on a part to fix my U3's feed screw problem.

This is the piece:



It is quite small, total length is 35mm.?
Large part is ? 20mm x 13mm and the rest is ?12mm x 20mm.
It will have a brass centre and will replace the OEM bushing once the feed screw receives a new, longer thread at that end as well as a new handwheel.

But I digress ...

I used to think I had my U3 properly/reasonably aligned.
After a rather long process and using thin shims, I eventually managed to achieve this result:



But I have run into a problem:



The distance between the points where the readings were taken is ~ 20/21mm.
And as you can see, the difference between them is almost 0.08 mm, with the larger diameter at the end.

Tomorrow I'm off to get a 180mm piece of precision ground/hardened 20mm steel rod and then see about finding someone to make the centers for me.
Can't do that on the U3.

That will/may put an end to any doubts wrt the U3 alignment.

In the meanwhile, I'd appreciate any comments the forum could offer with respect to this.

Thanks in advance.

Best,

JHM

Hello:

Mr. Pete ...? ... has two videos on making test bars ...

Indeed ...
I am a /huge/ fan of Mr. Pete and I have seen both videos. 8^)
He explains everything very well.

That said, most if not all of Mr. Pete's videos are directed at
enthusiasts who have or work with a range of tools well outside of what
the Unimat 3 is and can do.

He has only mentioned the Unimat 3 once, in the context of a "Buying a
lathe" video and "/... only to show you that lathes come in many
different sizes/".

In the first video you linked to, he shows a bar much like the one I
will purchase next week but don't have a granite surface plate to check
it. (yet)
The U3 cannot pass a 20mm bar and even if I chose to get a 10mm one
instead, attempting to make the centers on my 4-jaw would probably not
produce an accurate enough result for the test bar to be useful as such.

Thanks for your input.

Best,

JHM

Hello:

... off to get a 180mm piece of precision ground/hardened 20mm steel rod ...

I postponed the 2 hr. journey to the purveyor till I had someone with a proper lathe+skill to make the centers on the rod. for me.
Fortunately, I found a chap willing to do the job for a reasonable price and the bar will be ready sometime next week.

In the meanwhile and having the week-end to try alternatives, I set up this:



It's a 140mm piece of ~19mm rebar dowel found in a skip and cleaned up/roughed to size some time ago.
I had no aluminium stock at hand and as the rebar was probably grade 40 at best, I thought it would be easy to work on.
I put another center on it, roughed it to size again, made two fine cuts and then measured the diameter at each end.

With the readings taken (~ 110mm apart) and the difference calculated, I replaced the shims for the next size I calc-guessed would give me a better result.



The last of 8/10 attempts, using a pair of 0.23mm plastic shims gave these results:

• headstock end: 15.375mm
• ?tailstock end: 15.450mm
• difference: 0.075mm
• alignment error: 0.037mm

With a proper test bar at hand, I will hopefully be able to confirm these results.

Q: if confirmed, is this an acceptable result for a Unimat 3?

Can't leave out that all this took much longer than expected because I started using my new set of Taig "high speed steel" bits purchased from a dealer in the US.

After much grievance, it dawned on me that I had thrown away US$50.
It was a huge disappointment but also a lesson, at least for me.

The job was finished in a jiffy using a DCMT21.51 holder/insert purchased last year at Aliexpress.

I'd appreciate any comments on the results.

Thanks in advance,

JHM

If you have a decent dial indicator a 10mm bar will be fine. Remember,
the drilled centers don't have to be perfect as you will be turning the
test bar between centers anyway.

On 4/23/23 2:00 PM, Julius Henry Marx wrote:

Hello:

Mr. Pete ...? ... has two videos on making test bars ...

Indeed ...
I am a /huge/ fan of Mr. Pete and I have seen both videos. 8^)
He explains everything very well.

That said, most if not all of Mr. Pete's videos are directed at
enthusiasts who have or work with a range of tools well outside of what
the Unimat 3 is and can do.

He has only mentioned the Unimat 3 once, in the context of a "Buying a
lathe" video and "/... only to show you that lathes come in many
different sizes/".

In the first video you linked to, he shows a bar much like the one I
will purchase next week but don't have a granite surface plate to check
it. (yet)
The U3 cannot pass a 20mm bar and even if I chose to get a 10mm one
instead, attempting to make the centers on my 4-jaw would probably not
produce an accurate enough result for the test bar to be useful as such.

Thanks for your input.

Best,

JHM

--
Elliot Nesterman
elliot@...


"The finest jewel cannot disguise a flawed character."