Member postings for Steve355

Thanks all for the replies. That’s great, I won’t need to source a different arbor, and I won’t try to mill a keyway into it!

All I need to do now is work out how to get the mill out of the car.

cheers

Steve

Hi again

My wife does not need all that gardening stuff in the shed, so when I saw an old Burke horizontal mill for sale, at a good price and with tons of tooling, a stand and a motor, I decided to go for it. The Zyto and Dore Westbury are now both working fairly well so I need a new toy to fix up.

It’s still in the car, but I got the arbor out this morning, having cleaned up the cutters that came with it.

I was surprised to find the arbor had no key slot, despite most of the cutters clearly wanting one. Is this normal? Is friction enough to hold such cutters?

Or will I need to mill a slot in the arbor/get another one? Apparently it’s a Browne & Sharp #9 taper.

7/8 9 TPI BSW in steel

Unfortunately it’s not 7/8” cos I had to start again and turn off the first thread, but once I’d solved the problem (play in lead screw) it started working properly. But very nearly right, getting better every time. It actually holds a 7/8 nut albeit rather sloppy.

Edited By Steve355 on 02/12/2021 00:19:26

Thanks Howard and thanks for all your advice. 😎

Steve

Looking much more hopeful…

Here we go…l

So….. it feels much more solid and decisive. It hasn’t skipped at all. Much better.

This is a .236” (as suggested) pin with the end turned down further to 3/16 for the thread into the half nut.

it does still flex the lead screw upwards slightly as it engages. Not sure why - might be because I haven’t got the measurement Bob pointed out quite right. Or something. I will try to cut a thread before work tomorrow.

Right now I need a rest from the damn thing!

Edited By Steve355 on 29/11/2021 21:41:25

Edited By Steve355 on 29/11/2021 21:42:00

Bob,

Thanks very much for the suggestion. I have filed out the slots. I don’t have any letter drills but a 6mm drill bit seemed to be a sensible option, and so I have filed it so the bit is snug but runs freely throughout the length of the slot. They were not at all even or consistent previously.

Next step, make up a couple of 6mm pins with 3/16” threads on the end. I will probably go to hell for making a metric modification to an old imperial lathe, but needs must I suppose.

Cheers

Steve

That makes a lot of sense Howard. The thing that’s perplexing me though, is that there is no adjustment at the tailstock end - the support for the lead screw is cast into the bed. There is adjustment at the headstock end, but I unbolted it last night, but surprisingly the amount of adjustment available was very, very limited. Maybe 1mm of play up and down, essentially the play in the holes that hold the bolts. I was able to lift it slightly and re-bolt it, which seemed to place the lead screw parallel with the bed, as confirmed by a depth gauge.

I came to the conclusion that the adjustment available was only to enable the lead screw and bed to be parallel, and the vertical placing of the half nuts was done by shimming the apron.

Or something else, but I’m running out of ideas!

Pic shows the bolts I unscrewed,

Bob

it’s great to hear from someone who actually owns a Zyto lathe! It’s been a bit of an uphill battle for me, having little experience myself, and not knowing how the lathe should actually be. I’m sure they have all been modified over the years, and there would’ve been numerous revisions from the manufacturer as well.

Can I ask a question, what diameter are your pins, and what diameter is the slot?

My pins are 3/16, and several other Zytos I’ve seen look to have the same.

My slots are just under 1/4”, about 0.230.

Are there any shims between the apron on yours and the top of the carriage?

Another pic of mine with the pin in the same position as yours, looks remarkably like yours.

The problem really does seem to be the pressure that it is putting on the lead screw,

cheers and thanks for your input.

Steve

Dave

I’ve taken a look at the lead screw mechanism as you suggested. The lead screw itself has very little wear at .625 pretty much everywhere, so that’s good. Using a m&w depth micrometer, the distance to the lead screw from the bed is .614 at the tailstock end and .592 at the change gear end, so it is slightly slanted down at the headstock end. I’m not sure if 0.022 is enough to make a difference, but I may as well sort it.

I also realised that there is about 2mm longitudinal play in the lead screw, which I’d think could make a big difference. Again, I will sort that.

I have a feeling that all this started when I reconfigured the changewheels for the first time a couple of weeks ago. The V bracket that holds them was very stiff and took quite a bit of freeing up. Looking at the location of the change wheel bracket (whatever it’s called) right next to the lead screw adjustment, it’s easy to see that I could have knocked the lead screw out of alignment.

When I escape from the kids I will sort all these things out and see what difference it makes.

I don’t think so, as the upper half nut has the lead screw guard attached to it. It’s possible that was an aftermarket addition, but anyway if they were the wrong way around I don’t think it would even engage with the thread. I’ve had the nuts off and sat them on the lead screw and everything seems square and correct.

I got it working quite well this morning by measuring the displacement of the lead screw with no shims, then adding exactly that amount of shim to stop it happening (28 thou). I then added a 7 thou shim at the other end to stop it sticking on disengagement. That might be the solution for now. I will try cutting a thread tonight and see how I get on.

Medium term, I’m thinking of getting a 5/8”-8 acme tap and a bronze bar, taking off the ruined thread plus a bit on the mill, and then tapping, turning and cutting the bronze bar to fit. Then gluing or brazing on the new thread section. I saw a vid on YouTube of a chap doing something similar.

Steve

Edited By Steve355 on 27/11/2021 13:30:37

Right I think I am getting there, extreme persistence paying off perhaps.

Rule 1 the half nut must be free of burrs and obstructions

Rule 2 the nuts must engage and cause no movement of the lead screw. If they do they are engaging at different times and the carriage may jump out of thread. To adjust this the left side of the apron can be shimmed.

Rule 3 the nuts must be absolutely perpendicular to the lead screw, else the half nuts will stick in the lead screw thread when disengaged. To adjust this, the right hand side of the apron can be shimmed. Too high and the top nut sticks, too low and the bottom nut sticks.

Rule 4 (which I am predicting will be the next problem) the lead screw needs to be parallel to the slideways of the lathe.

Different shims at both ends.

Edited By Steve355 on 27/11/2021 09:39:37

Edited By Steve355 on 27/11/2021 09:40:22

Edited By Steve355 on 27/11/2021 09:40:36

Edited By Steve355 on 27/11/2021 09:42:06

Edited By Steve355 on 27/11/2021 09:43:17

Hi Martin, yes and yes, you kindly provided that document to me a while back. The trouble has been that when I engage the lever, the half nut hasn’t been engaging, it skips and engages 1/8 of a wheel turn after. If you see the pic of the upper half nut above, frankly it’s amazing it works at all.

I watched a really excellent vid by Joe Pie yesterday which has helped me to much better understand how half nuts and lead screws work in detail.

https://youtu.be/kESm2Kozb-4

So essentially what’s happening is the cam is moving the half nuts into a position where they will engage *next* time the lead screw is in the right position, and creating the pressure to do so. The lever is not pushing the half nuts into position directly. That explains why the pins are “too small” and there is play in the cam. There needs to be so it can accommodate the half nuts being in or sitting on the thread.

my half nuts look like they are engaging at different positions where they can, hence the “jump” that occurs. Here’s the jump by the way….

Steve

Closer look….

Bottom half nut in good condition

Top half nut with 2 1/2 knackered threads. It also has a threaded hole bored in it to accept a screw which hold the lead screw guard. It looks worse in the pic than it actually is… and indeed has worked like this until recently. But clearly it needs renovating.

More importantly, there is a burr on either end of the top half nut which could be impeding the correct engagement and disengagement of the lead screw.

There is also some “bobbling” of the metal surface next to the dovetail, which has probably always been there, but it may not help the half nut to move smoothly when the gibs are tightened.

So, plan A is get to work with a file in the morning and fix these bits as best I can, and see what difference it makes.

Plan B is to renovate the top half nut, which clearly needs doing. I’m getting some ideas for how to do that.

I agree Howard. So I have had it all apart again and this time I have worked on adjusting the gibs, so that the is no slop in the movement of the half nuts. Now gravity plays no part and they basically stay where the lever/cam mechanism puts them. This removes another variable.

I’ve been looking very closely at how the half nuts disengage. The lower nut disengages properly, but occasionally, the upper nut sticks. When the apron is off, now I have adjusted the gibs, the nuts behave in a very predictable way, with no movement other than that caused by the lever.

So I think the upper half nut must be catching somehow.

The whole mechanism that supports half nuts is interesting. When the half nuts are closed, they stand a 50-50 chance of landing on a trough rather than a crest of the lead screw. Usually, one doesn’t notice this, the lead screw turns and the half nut just slips into the thread. For me, for some reason, that isn’t happening correctly.

The top half nut is in bad condition with 2 of 8 threads basically stripped. Whereas the lower half nut is in good condition.

I have also turned around the lever to match the other Zyto lathes on YouTube. This seems to make the pins look the right size.

Thanks for the replies….

When I take it to bits again later that’s the 4th time today I’ll have taken it to bits!

I’ve watched several YouTube videos of people restoring Zyto lathes this afternoon. All of them have 3/16” pins, but all of the pins seem to fit, and the cam looks different. I think mine is either a replacement, or a previous owner has messed with it. None of them have springs.

I think Howard, your idea of turning down some thicker pins is the easiest thing to do there.

I still wonder how to fix remake half nut threads, but that might be a project for another day, presuming it works reliably once I’ve fixed the basic mechanism.

Stupid question, but for these styles of lathes, is “down” usually engaged or disengaged for the half nut?

thanks

Steve

Even though I seem to have made progress, there is still a problem with this lever in that the engagement position is too low (about 9 o’clock). Also, it has a system whereby a spring is I think designed to cause it to lock in the on or off positions. I will post some pics later. By the way, yes, I have fixed the pins, they are straight now 😎

It was moving up. So I have shimmed the apron with feeler gauges, and it seems (touch wood, pending further testing) to have cured the engagement problem. I’ve engaged it now maybe 30 times and hit the number on the thread dial indicator every time, no jumping or skipping.

it it still stiff on disengagement, which is probably the same problem in reverse - one nut disengaging but the other not. I will look into that further.

Thanks for the tip.