Retlas

[Ian S C]

With my method, I'v used it in steel, and aluminium con rods, and yes for my own design of hot air engines.  The hole in the con rod, and the outside of the bronze bush are oval, and instead of a slitting saw, I cut the cap, and bush with the mini power hacksaw powered by one of my motors, in fact the first one made was for the motor that was driving the saw. This is the saw on a different motor.
Ian S C

[Chipmaster]

Con rod with the shaft machined round and tapered

Building Retlas 544 by Andy, on Flickr

Setting up a rotary table to mill the profile of the little end. This was the first time I used this gadget - Coaxial Centring Indicator, that I bought over a year ago. The rotary table was bolted down first then centred by moving the x and y axis. My usual method is to use a centre in the milling mc spindle to guide the position of the rotary table before securing it to the milling machine table.

Building Retlas 545 by Andy, on Flickr

Andy

[Chipmaster]

I forgot to take a picture of profiling the little end of the con-rod on a rotary table. Here's a picture of the rod after milling round the little end and some filing to blend it in with the round shaft.
Building Retlas 550 by Andy, on Flickr

Andy

[Chipmaster]

Making the bronze big end bearing.
The first thing I did was solder a piece of cored phosphor bronze onto a 5" length of brass bar that was about 9/16" diameter which could be held in a quick change boring bar tool post.
Building Retlas 552 by Andy, on Flickr

The bronze was turned down just enough to clean up the surface.

Building Retlas 554 by Andy, on Flickr

The centre line was marked and set up on the lathe for a 1/16" thick slitting saw to saw to the left just touching the centre line.
Building Retlas 555 by Andy, on Flickr
Building Retlas 557 by Andy, on Flickr
I used a hacksaw to separate the smaller half of the bearing then soldered it back on.
Building Retlas 558 by Andy, on Flickr
Building Retlas 559 by Andy, on Flickr

Returned to the lathe mounted in a multi collet chuck to ensure accuracy then bored out and reamed to fit the 5/8" crank pin. The jubilee clip was to help the soft solder hold the two halves together.
Building Retlas 563 by Andy, on Flickr

Taking light cuts because of the risk of the soft solder coming apart, the bearing was machined to fit the con-rod  then parted off.
Building Retlas 565 by Andy, on Flickr
Building Retlas 567 by Andy, on Flickr

Turned round and glued onto a short 5/8" bar so I could turn a bevel on the mouth of the bearing.
Building Retlas 570 by Andy, on Flickr

Heated up so the shells fall apart, the brown stain is the residue of the burnt Hafix glue
Building Retlas 573 by Andy, on Flickr

Cleaned up and fitted to the con-rod.
Building Retlas 575 by Andy, on Flickr
Building Retlas 579 by Andy, on Flickr

Assembled on the crank shaft.
Building Retlas 574 by Andy, on Flickr

The bearing is a good fit, there are a couple of slightly tight spots that I will deal with, probably needs a little scraping here and there or I could leave it to bed down when the engine is being run-in. Anyway, I'm pleased with the result. Now I need to work out how to lubricate the big end bearing.

Andy

Andy

[10KPete]

 

Very nice!

Pete

[Chipmaster]

Thanks Pete.
To find the what was causing the tightness I applied Stuarts Micrometer Blue all over the bronze bearing surfaces and assembled the con-rod on the crank pin rotated the bearing then took it apart to see where the Micrometer Blue had been rubbed off indicating high spots. It turned out that a bit more work on the arris was required, that is more bevel on each end of the bearing. Now the con-rod swings round on the crank pin with no binding at all.
Andy
Building Retlas 586 by Andy, on Flickr

[10KPete]

 

I love spotting!

Pete

[Chipmaster]

Pleased to hear you enjoyed spotting round the arris
Andy

[Chipmaster]

Some pictures of the trial assembly of the con-rod. I had to file some of the base away to clear the con-rod at the three and nine o'clock positions. The big end bolts are temporary, I intend to have the bolts coming up through the big end cap with the nuts above the big end. This follows the original Gardner Vertical arrangement. Thanks for the info Jason, I think it will make the engine easier to assemble,
Building Retlas 589 by Andy, on Flickr

Building Retlas 593 by Andy, on Flickr

Building Retlas 594 by Andy, on Flickr

Andy

[Jasonb]

Looking good

[Jo]

I'll take it slowly because I have found the results produced by my taper turning attachment rather variable  . The attachment looks to be in good condition and is well lubricated so perhaps a worn cross slide feed screw is to blame? I would be interested to hear of other members experiences with taper turning attachments.
Andy

I have the same taper turner on my Master: I fitted it brand new having found it in the College's stores about 20 years ago. It gives me no problems and is very good  . If the feed screw is at fault it should show with normal turning.

  Andy why is the skirt of the cylinder liner sticking below the main casting.

Jo

[Chipmaster]

Thanks for your response about the Colchester taper turning attachment Jo, reckon I'll dismantle the attachment and cross slide and examine all the parts when I'm in the mood. Does your cross slide feed screw have much backlash? On mine I can turn the cross slide handle and the dial reads about 30 thou difference between the cross slide actually moving forwards or back. The lathe came with a spare cross slide feed screw which appears to be un used, unfortunately it's the standard screw which was probably retained when the telescopic feed screw was fitted for the taper turning attachment.

The cylinder liner/minutiae, I suppose you've been checking the drawings and reason that the liner should only project by about a sixteenth of an inch? Well, the liner is exactly the right length but the cylinder yoke casting was shorter than required and there was never enough casting to allow 4.5/16" over the faces as specified in drawing No 200. Cleaning up the cylinder casting was kept to the absolute minimum, anyway perhaps I'll end up with a higher compression GT version. Reckon I'll be able to trim bits if necessary.
Regards
Andy

[Jo]

Silly question: Is it the same backlash all the way across? In which case have you tried adjusting the antibacklash cross slide wedge?

Jo

[Chipmaster]

Not a silly question at all Jo.
The backlash is virtually the same all the way across. I have adjusted the gib strips from time to time but I haven't adjusted an antibacklash cross slide wedge, don't know if the Chipmaster has one. I'll have a look in the manual but I don't recall seeing a reference to such a thing. Mind you the original Colchester manual that I had with the lathe doesn't say much about maintaining the lathe.

Andy

[Alyn Foundry]

Hi Andy.

By gum, this forum moves quickly! I hadn't noticed your recent posts.

That's an interesting development regarding the cylinder protrusion, you are the first to mention it. The drawings were made from Vincent's first build and the yoke pattern was a rather flimsy wooden one. I remade an Aluminium master from it and the loss will be partly due to shrinkage ( 3/16" per foot-linear )  All subsequent patterns were made with double shrinkage so that the final castings would be to size.

Re backlash. Does your cross slide nut have any adjustment ? They are usually part split with a cap screw to close the gap, reducing thread backlash. Just a thought.

Kind regards, Graham.