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Picking it up.

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bhowden:
Re missing steps.  I have not seen a lot of discussion on acceleration /deceleration profiles with respect to the steppers.  If you assume the lead screw always "engages" with the spindle stopped you might be safe enough assuming that the inertia of the spindle will be higher than the lead screw and the stepper will never be asked to change speeds faster than it is capable of but if you engage /disengage the lead screw while the spindle is turning I expect you will have some issues.  The brief look around I took shows the subject can be quite complex if done correctly but there are some assumptions that make the problem more approachable (eg assume linear acceleration and use conservative values)  The other issue with engaging and disengaging is going to be back lash if you are changing directions.  Possibly an issue with threading without a thread dial, depending on technique.

Brian

vtsteam:
Brian, this is an intended replacement for change gears, and it will use a threading dial and halfnut for engagement with the leadscrew turning. I like to find things out for myself. I suspect we all do, once involved in a project.

And I always treat my projects as experiments. Not certainties They generally lead to new discoveries, at least for me. Often through Plan B .....and C. And in doing that they quantify theory where it does indeed apply -- somethng rare online. It's easy to argue a generalized internet theory. But hard to prove it applies in a specific case.

If at any point I find it doesn't work, I'll either work my way around it, or change direction. Not a loss either way.  Personally I think this experiment is worth a try.  :beer:

DavidA:
VT,

A few pics of the Mason baby lathe during construction.

The tailstock assembly has been pulled apart as it need some modification.

Most of the assembly of the bed was done,  then I discovered that the reference bar (1/2" silver steel) wasn't quite straight.

Dave

vtsteam:
I've never seen that one before, David. How big is it?

By reference bar do you mean the bar  in the headstock, or a different bar, like a straightedge?

How do you use the reference bar?

DavidA:
VT,

The lathe is 16.5" overall. I think there is 1.5" between the bed and the centre line.

The whole thing is built up from 2" and 2.5" X 1/4" BMS, Except the headstock bars which are 1" x 1" BMS

I had to reduce the size of the pictures dramatically and so they don't expand very well. But it is a fully functioning lathe. Full set of change wheels for screw cutting; naturally only the finer threads. Back gear is there.
It has a dog clutch on the leadscrew. If you want to fit it.
The mandrel has a Number 1 Morse taper,  as has the tailstock. A back plate is also described.

The reference bar is that length of 1/2" silver steel that is sticking through the headstock. The whole machine depends upon this bar,  and it must be true. Mine, it turns out,  wasn't.

Mason goes into great detail on how to align the bed. You may find his method useful.

Basically you start with only one bolt through the front headstock bar; the top one. At this stage the holes in the front side  plate only are drilled, and the top hole of the front headstock bar along with it's matching hole in the back plate.

You can now slip a bolt through the top hole and lightly nip it up. You will realise that you can now pivot this headstock bar around the bolt. The reference bar will rise and fall.

You lay the bed on top of the side plates.
Put the rear headstock bar in position and feed the reference bar through both bars,  as in  the picture.

Now comes the clever bit.

You move the bar up and down until it is exactly parallel with the bed. He uses blocks and feeler gauges to get it spot on at both ends of the bed. It could be better done with a dial guage mounted on a sliding block. But his method works fine.

When it is spot on,  you use clamps to lock the side plates against the headstock bars. Re check the reference.

Then drill through the other three holes through the head stocks and the rear plate. Bolt them up.
You centre line is now fixed in the vertical.

You then fix the bed plate to the rear side plate with one screw; the rear one nearest the chuck end.

Using a couple of spacers you lay the whole thing on it's side,  resting on the edge of the bed plate, on a flat surface and pivot the body around the screw while checking for parallel between the reference and the surface plate.
When this is parallel it means that you have the edge of the bed true to the centre line of the lathe.

Now it is true in both axis.

Clamp up the bed to the side plates and scribe underneath the bed on each side of each side plate. (blue it first)

Remove the bed, drill the remaining screw holes in the bed  plate (from the underneat face, carefully between the lines you scribed. Refit he bed with it's one screw and, after checking again, drill down into the edges of the side plates, tap and then countersink the bed. screw it down.

Job done.

I strongly recommend getting a copy of this book even if you don't make the lathe. it is full of good ideas.

Oh yes,  You can then align the tailstock on it's base by sliding it onto the end of the bar. If your bar is straight, it must then be in alignment with the headstock.

I now it may seem complicated the way I describe it,  but really it is quite logical and easy. You just need to be careful.

Dave.

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