Thread: Is this a valid test?

Ok based on your comments I've tossed the first design, the current plan is to make a spider for the end of the spindle(something that is on the todo list anyway). Then add a collar that holds the wire. That will give up/down and front/back adjustment(plus have the tailstock if needed). I'll use the saddle as I have to put it back on to make the parts I need anyway. On the tailstock end I was planning to have a bearing so the wire would run over it to go vertical and then have weights for tension. I'm thinking now that that might be a little over the top.........I'll see how its looking.

I'm using the wire as I dont(as yet) have a straight edge have a straight edge 1300mm long. I'm currently interested in seeing how close it is.(Despite RC's warning I think I maybe suffering from a lack of planning). To see if its worth scraping the carriage to the bed or if I need to start with the bed(one day). I've been resisting test cuts as it removes me from the equation , but as its going back together I guess it wont hurt. Based on how nasty things look I'll work out what I need to do next(or more likely you'll work out what I need to do next lol)

From what I've seen on the test bar I'd say its not so great............... but where do you stop? lol 99.999% of the things on make dont matter much.

Originally Posted by Machtool

You might have noticed, I have a large ground disc as the mount, that’s so you can clock it to vertical.

This is the one part I didnt get. I understand the need for vertical. This is the only picture I have of your scope. Do you mean you level the disc , then put the scope on top?

Thanks

Stuart

Originally Posted by Stustoys

This is the only picture I have of your scope. Do you mean you level the disc , then put the scope on top?

No wonder that Pic is leading you astray. I’m surprised its mounted like that. I must have lent it to someone. Normally it never comes off the mount. That bottom shroud, I should have thrown it out years ago. I’m yet to use it.

The mount I made, is just a ground disc, with a 10mm piece of shafting , for a standard mag base clamp. Then I just clock the disc horizontal.

Attachment 210517

Attachment 210518

Regards Phil.

*I remember who I lent it to now. It wasn’t a forum member.

Wow Phil, Brilliantly simple! I was sketching far more complicated things that likely wouldn't have worked half as well.

Well the lathe is back together and the spider is half made........... just one problem in the tray the apron was stored in there is one ball bearing about 8mm. I'm stuffed if I know where it came from...... all the detents still work, powerfeeds work, halfnuts work...

Stuart

Stu.

The other thing I should have said. Where that shroud screws off, there’s not much thread, but just enough, there’s a lock nut under that disc to keep the scope tight. You don’t want it loose.

Down in the guts of the scope, under the eye piece. There’s a tiny retainer ring that holds the graticule with the increments on it. That retainer come loose once, and that optic was floating. Drove me nuts, took me half a day to work out why I couldn’t get this linear rail straight.

Originally Posted by Stustoys

I'm using the wire as I dont(as yet) have a straight edge have a straight edge 1300mm long.

Is that a metre between centres, and 300 for a tailstock? If a bloke was to lay his hands on something like this one weekend? A cylinder square 900 long x 200 diameter. I’m pretty sure this one has safety centres. And is gospel straight.

If you where to drop that between centres. And set your tailstock the same as your headstock. That will show you straight.

Sorry about the crap photo’s, I took them with my phone out on site this morning.

Attachment 210680


Attachment 210681


Attachment 210682


Regards Phil.

Hi Phil,
Mine had the same problem I think, something was certainly loose inside but I forgot now what it was. Not much else in there it could have been.

I think its a little longer that 1000mm but not enough to worry about.
Thanks for the offer, I'll more than likely take you up on it one of these days, but I'll have a look with the wire first just to get an idea what I'm dealing with.........maybe I could just use a rule? lol
To back up a little I'll try the S/S wire first and see how it goes, I'll try the piano wire if its no good.

The wire jig is finished. Pictures of the spider and bush fitted in the sipder and the bush that fits in the tail stock(I was worried that with the thicker wire I might pull the chuck out ot the tailstock).

Now I just need to make a "nut" to hold the extra lens on the scope.

Stuart

Well I have some numbers.

After stuffing about trying to pull the tailstock to tighten the wire(I ditched the weight idea) it dawned on me to use the carriage.

After getting the light in just the right spot with the stainless wire you can get a bright line less than 1/4 a division wide.(sorry about the picture its the best I could get but it looks way better than that.

So the numbers 51 turns of the carriage handle from end to end(880 normal carriage travel, 1020mm max, though you'd have to take the leadscrew off)
Turns of handle=Reading
0=99.5
10=99.5
20=97.5
25=96.5
30=96.5
40=97.5
50=99.5

3 divisions, now if my earlier math is correct thats 0.001".

I'll check it again in the morning.

Scraping the carriage to that wouldnt be terrible would it?

Stuart

Originally Posted by Stustoys

Well I have some numbers.

After stuffing about trying to pull the tailstock to tighten the wire(I ditched the weight idea) it dawned on me to use the carriage.

After getting the light in just the right spot with the stainless wire you can get a bright line less than 1/4 a division wide.(sorry about the picture its the best I could get but it looks way better than that.

So the numbers 51 turns of the carriage handle from end to end(880 normal carriage travel, 1020mm max, though you'd have to take the leadscrew off)
Turns of handle=Reading
0=99.5
10=99.5
20=97.5
25=96.5
30=96.5
40=97.5
50=99.5

3 divisions, now if my earlier math is correct thats 0.001".

I'll check it again in the morning.

Scraping the carriage to that wouldnt be terrible would it?

Stuart

Hi Stuart,
I have not quite grasped exactly how you where going to achieve your test with this method....until i saw the pics in your last post. I'm guessing a carefully set DTI couldn't really be used on the wire as it would deflect the wire a tiny bit? It is a very clever and easy method to create a straight plane in otherwise out of straight world.

Originally Posted by Stustoys

Scraping the carriage to that wouldnt be terrible would it?

Thats really good work Stuart. Every thing has errors. If your are a thou straight, the saddle will only be a 1/3 or 1/4 of that lenght .Local error under the saddle is in the order of third or quarter of that.

Keeping it real, you can scrape to that. Theres not alot you can do about it anyway. Theres no facility to move the bend out of the middle. larger machines do have, they have side pusher jacks on the side, so you can tweak a bend out of the bed.

Phil

Looks interesting Stuart
Are you going to set up a mirror or some such to see what it is doing vertically as well? I guess there will be some catenary effect in there, but with light wire that is tight, it shouldn't be much.

Michael

Hi Ewan,
I must say I'm surprised. I thought I'd try the DTI just to see how bad it was. I had a play with my cheap DTI and it was looking ok so I got the good one out. Its useless for some reason(maybe because it has such a tiny contact ball). So I put the cheap on back on and although the wire moves about 0.003" as the DTI is moved over it the readings are surprisingly consistent and the answer I came up with is 0.0018". A longer tighter wire may improve things but could you ever trust it?

Hi Phil,
Thanks.
I could always scrap the bed......... maybe next year lol
As you say I think its "close enough". If I line the headstock up with the first half of the bed it will be damn close in between those two points. I think I've only used the other half the bed about three times... other than as a handy place to keep the carriage when I want to get at the work piece lol
I think I can get back onto the close slide and checking the headstock alignment.

Oh and at night I can get an view like this which works ok as well.

Stuart

Hi Michael ,
I hadn't thought of a mirror! At least the wire would move the right way. I was going to check the vertical just for giggles as I'm not that worried about it.(of course if I had half a brain I would have checked it while I was setting up the ends). It must be pretty close as the depth of field on the scope cant be more than about 0.1mm

I think a "proper" scope might have better depth of field as I believe the extra power comes from the eye piece.
Oh Phil, Does the wire in your scope move backwards? or did they put enough lenses in to make it move as the right way?

Stuart

p.s. I think the error is even in the right direction. i.e. the bed bends towards the work in and middle

Originally Posted by Stustoys

Oh Phil, Does the wire in your scope move backwards? or did they put enough lenses in to make it move as the right way?

Most definitely back to front. You have to do the opposite of what the scope tells you..

I find it better if you can learn to do a hand stand on top of the scope, so what you see, is what you get. {/joke}

Phil.

Tried that, put my neck out
I should add that although it is far from finished the cross silde feels much better.
I will make a mount like yours and it will make life much easier.

Stuart

Well now what?

I measured the vertical error this morning and came away from that happy enough.
measured in both directions to be sure I hadnt lost 0. Bigger numbers mean the wire is lower(no surprise there after you have seen them). reading is 0.001" as I cant use the "booster" with the mirror. I think there is also some parallax error going on so the 0.0005" are best guess.
0=118
10=119.5
20=120
25=120
30=120
40=119.5
50=118.5
40=120
30=120
25=120
20=120
10=119.5
0=118

Then I thought I should write all this down as I might want to look back on it one day. I also realised I hadn't checked the lathe for level before I started all this and that turned up my next "problem"? Moving the carriage from one end to the other moves the level 5 divisions. It wont stop me from getting back to the crosslide but its something I'll have to have a think about.

Sorry about the level pictures they are 1 second exposures

Worrying about nothing? time to make a new stand?

Stuart