9 x 20 half nut problem

[savarin]

Made new rubber wipers that have the added bonus of holding a bit of the oil back in where it should be.
Eagerly awaiting the new half nuts being sent to me from hman along with a couple of other bits. How awesome and amazing is that.
That beats waiting for 16 weeks and probably longer considering the Chinese new year will be upon us by the time they got round to sending the order.

 

[savarin]

Whilst waiting for the half nuts I've decided to extend the cross slide screw for a bit more travel, add real bearings to the shaft, make it M10x1 to make the travel calcs easier. The original M8x1.25 thread is very worn in the middle with a lot of backlash but very firm at each end of its travel so it does need replacing.
What would be the best material to use for a new lead screw here?
I have a heap of stainless rod I could use, would this wear ok do you think?
And would brass be ok for the nut?
I have a bit of scrap from a marine pump that I think is bronze of some type, maybe I should cast a chunk for the nut from that if brass is too soft.
Made a start on the new larger handle from a zinc alloy ingot and on the vernier ring and dial from a small length of 60mm dia leaded steel from somewhere (I think it was a drop I was given)

 

[savarin]

Once you start fettling you just cant stop.
I have a length of alloy 60 x 100 mm long so that will be the bracket, the handle I've turned from a zinc alloy ingot.
I made a 100 segment circle scale held in the end of the spindle as an indexing aid to scribe the 0.01mm divisions.

The saddle stop is clamped with a "G" clamp so the divisions are all the same length.

Once I finished the divisions I knurled the end,

then bored the middle out with a hole saw then parted it off.

the finished dial sans numbers sitting on the handle with a very smooth fit.

The bearing on top will be in the extended bracket.
I know this flexi lathe cant hold this kind of accuracy but I though with the 1mm thread and 100 divisions on the lead screw it will make the length calculations easier (I hope).
I'm still uncertain what material to use for the lead screw.
I have enough stainless I could use but am unsure if it will wear ok.
The nut will be either brass or some cast bronze if I melt it.

 

[savarin]

There are times when I hate turning, reducing the centre of the extension support bracket could only go one pass at a time due to this.

Any way the parts from John Herrmann (hman) have arrived so its geterbackproper.
I took a lot of care getting everything adjusted to as spot on as I could and ensuring the half nuts closed from both sides equally took a bit of fiddling but we got there.
Next I added the brass brush John sent, so simple, so effective, I love it

and with the cross slide shield I think swarf will find it very difficult getting in there.

with the half nuts replaced the old ones are virtually smooth on one side and the other one has half the width of the thread worn away.
I really hope all the care I took ensuring they clamp up equally will prevent this from happening again.

Does it all work now?
Yep
single point M8 x 1 in stainless.
These are for the bearing clamps on the binocular.

 

[savarin]

Started on the cross slide shaft but its a long process turning that down from 16mm to 10mm.
However, like all my projects I've been side tracked again.
I'm attempting to make a vernier scale, no real reason in this instance just to see if I can.
The idea is to add a vernier scale to the cross slide dial of my lathe.
On a flexi 9x20 its a bit of nonsense but what the hell.
I have engraved 100 divisions around the dial using a scale I printed off from this site.
http://www.cgtk.co.uk/metalwork/reference/divider as you can see above.
This hopefully will give me an advance of 1/100 of a mm of cross slide travel per division so with the vernier theoretically it should advance 1/1000
I'm thinking if I print off a scale with 90 divisions to the same diameter size as the 100 scale and use that to engrave another dial but just use 20 divisions this should give me 9 divisions in the space of 10 divisions on the original scale.
A quick test by printing both scales and overlaying them to see through the 90 to the 100 underneath seems to bear this out as with the zero on each scale in alignment the 9th division of the 90 scale sits on the 10 mark on the hundred scale.
or should it be a 110 scale where the number 10 sits on the 9 of the hundred scale.
Which one would be the correct version?
Am I on the right track here or just blowing bubbles?

 

[Bob Korves]

Am I on the right track here or just blowing bubbles?

Resolution and accuracy are two different concepts. Increasing resolution does not necessarily increase accuracy. On your smaller Chinese lathe, I hope it will make you feel better...

 

[savarin]

As I said Bob, On a flexi 9x20 its a bit of nonsense but what the hell.
It will look cool and as we all know - cool beats practicality.

 

[savarin]

I eventually used the 110 segment scale, it gives 10 divisions in the space of 9 divisions on the main dial.
Heres all the parts

Assembled

Its a nice smooth action with the two bearings.
I'm really happy with the M10 x 1 mm thread, the longest I've cut and very smooth

Now I have to mill off the excess aluminium from the extension bracket and I haven't worked out how yet.

If you look closely you can see the brass shim where I over bored the bearing recess.

 

[BROCKWOOD]

Looking good! I like the way you are tightening your specs & correcting your dial. Mine shows 80 divisions for 0.010 of movement per revolution. Gonna follow your lead on this!

 

[hman]

Now I have to mill off the excess aluminium from the extension bracket and I haven't worked out how yet.
View attachment 281568

Consider this ... There's really no need to continue the dovetail profile on the part. It has no guiding or alignment function. I think all you really need to do is clear the slide. So you might consider cutting on something like the yellow outline illustrated below.