Author Topic: Retlas (Read 92210 times)

Chipmaster · « **Reply #135 on:** March 21, 2016, 06:41:43 PM »

Hi Graham, I've been wondering where you'd been.
Re my protrusion, I noted the lower height of my cylnder yoke casting early on in this build but reasoned I could easily compensate for that elsewhere on the engine, probably by shortening the piston if necessary so I'm not concerned by it.

My Colchester Chipmaster, built in 1969, has a plain bronze nut propelling the cross slide. I have checked a manual that refers to an anti backlash device incorpoated in the nut, there appears to have been either an option or a later spec with the anti backlash device. I'll post a drawing from the manual after dinner.

Andy

Chipmaster · « **Reply #136 on:** March 21, 2016, 08:42:37 PM »

Jo, its bad enough being taunted that I seem to be missing a DRO, now I'm missing an anti-backlash nut as well

.

Here are scans of two Colchester Chipmaster Manuals, the first scan is from the original August 1969 manual that accompanied my lathe Serial No G4912, it doesn't show an anti-backlash nut.

The second scan is from a manual that covers lathes from serial No 6994 onwards in which the anti-backlash nut appears to be an option.

Graham - I can check to see if anything is loose otherwise there's not much I can do. I'd like to know how much backlash other lathes operators encounter to see whether I've got a problem. I always pull the toolpost/cross slide towards me when I use the feed screw to advance the cross slide and get on pretty well. Its taper turning that causes me grief.
Andy

Andy

Jo · « **Reply #137 on:** March 22, 2016, 10:37:25 AM »

This is one of the spare sets of standard antibacklash nuts I have for the Master and the standard lead screw and its nuts below it. These are 8278-1 ( imperial ) in the bag is the wedge. There is a different part number for the ones to go with the taper turner

I m not sure if a set of these would fit the chipmaster

Jo

Alyn Foundry · « **Reply #138 on:** March 22, 2016, 11:23:53 AM »

Hi Jo.

Is the top nut in two pieces? Suggested by the tape.

Hi Andy.

My Le Blond RP was a " Lend Lease " machine from WW2 and has worked hard, it was rebuilt by Alfred Herbert in 1954. I've had it for nearly 30 years and coped with the cross slide backlash by doing exactly the same as you. Some years back I reduced the backlash by sawing the nut and fitting a couple of Allen cap screws to tighten it. Incidentally my lathe never had a top slide just a massive 4 way tool post hence the ridiculously heavy cuts it can do. What's really nice is despite her age she'still holds decent accuracy.

Kind regards, Graham.

Jo · « **Reply #139 on:** March 22, 2016, 11:43:36 AM »

Yes Graham under that tape is a pair of the same nuts you see on the screw below.

Jo

Chipmaster · « **Reply #140 on:** March 22, 2016, 02:55:38 PM »

Re: Cross Slide backlash.
Jo & Graham, I have found tightening the bolt that secures the feed nut to the cross slide effects a remarkable improvement, mine was loose!

I've arrowed the bolt in this diagram, now I wonder whether that will improve the taper turning?
Andy

Alyn Foundry · « **Reply #141 on:** March 22, 2016, 03:36:55 PM »

Hi Andy.

Well at least it's fixed now.

My feed screw nut locking device is visible, you can see it rock when loose. Now anyone got any ideas on how to remove 200 thou backlash from my Knight Jig borer?

Kind regards, Graham.

Jo · « **Reply #142 on:** March 22, 2016, 05:04:10 PM »

At least it was a cheap fix

. I'll put my spares back in their hidey hole.

Jo

Chipmaster · « **Reply #143 on:** March 22, 2016, 06:09:16 PM »

Thanks Jo, I'll measure the diameter of the Chipmaster cross slide feed screw for comparison with your Master feed screw. They will probably be different sizes, I'd expect the Master's screw to be thicker.
Andy

Chipmaster · « **Reply #144 on:** March 22, 2016, 06:12:28 PM »

I'm about to machine the piston ring grooves in the piston and apart from size which isn't specified, I'm trying to decide whether to use two rings or three just because the plans leave the choice two or three, "up to the preference of the owner".
So far all my models have used two and run well. Can anybody suggest whether two or three rings are likely to make any difference to the Retlas?
Perhaps I could machine three grooves and have the option of leaving the bottom ring out.

Andy

Alyn Foundry · « **Reply #145 on:** March 22, 2016, 06:29:00 PM »

Hi Andy.

My answer now, based on years of practice making piston rings would be just two. When the Retlas appeared we were but novice's our piston rings were **** !! Over time we found that a square section, 90 X 90 thou with a groove depth of 95 thou worked the best.

If I were to try now I would probably recommend " Viton " " O " rings, as the latest generation are rated at 200 C+ working temperature. I have just one in my Gardner, it works a treat !!

Kind regards, Graham.

Chipmaster · « **Reply #146 on:** March 24, 2016, 12:01:52 AM »

Jo, the cross slide feed screw on my Chipmaster measures 0.5625" ~ 9/16" diameter. How does that compare with the feed screw for you Master lathe?

Andy

Jo · « **Reply #147 on:** March 24, 2016, 01:29:51 AM »

$:-\$ Even without going and measuring I know that is a lot smaller diameter.

Jo

Chipmaster · « **Reply #148 on:** March 24, 2016, 07:05:57 AM »

I thought there would be a difference Jo. On eBay I see a seller in Cardiff 'reltub34' occasionally sells cross slide feed nuts for Colchester lathes, they are listed as different items for the Chipmaster and Student lathes
http://www.ebay.co.uk/itm/Cross-Slide-Feed-Nut-to-Fit-Imperial-Colchester-Chipmaster-Early-Bantam-Lathes-/201532317174?nma=true&si=Yf1CPEsT23o9%252FAg%252BZbWqDlLsACU%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
I would like to have a spare but I'm not keen on sending my feed screw off in the post.

Andy

Chipmaster · « **Reply #149 on:** March 24, 2016, 08:01:03 AM »

The casting used for my Retlas piston came from Graham Corry - Alyn Foundry.
Graham said it was left over from their Hornsby Ackroyd project and would suit the Retlas. The pictures show machining the piston and using a Vee block with clamp to ensure the gudgeon pin is at a right angle to the central axis of the piston. I failed to take pictures of machining the two piston ring grooves using a 2mm wide parting off tool.

Retlas piston drawing

206 Retlas Piston by Andy, on Flickr

The casting had a chucking piece.

Building Retlas 595 by Andy, on Flickr

The gudgeon pin bosses were only just sufficient for a 3/8" diameter pin. After careful marking out the casting was held in a Vee block mounted in a 4 jaw chuck to bore and ream the hole.

Building Retlas 596 by Andy, on Flickr

Centre drill used to ensure drilling continued in-line on the other side.

Building Retlas 597 by Andy, on Flickr

Building Retlas 598 by Andy, on Flickr

Building Retlas 599 by Andy, on Flickr

Building Retlas 600 by Andy, on Flickr

Building Retlas 601 by Andy, on Flickr

Building Retlas 604 by Andy, on Flickr

Building Retlas 605 by Andy, on Flickr

Andy