curved T nuts

[Poloris]

Every time I swung my lathe topslide around to thread, one of the nuts rotated in the slot entry hole and jammed so then I had to take the topslide off and sort it out.
Now Ive made non-rotating T nuts.
I thought it would be a easy thing to do on a rotary table, not so.
Anyway the jobs done.
Mark

[Michael G]

They look the part so well done. I've seen all sorts of bodges arrangements used to avoid making proper T nuts for circular tracks, such as these examples
363098
Another method that works is strapping some stock onto a lathe faceplate.

Michael

[Oldneweng]

Every time I swung my lathe topslide around to thread, one of the nuts rotated in the slot entry hole and jammed so then I had to take the topslide off and sort it out.
Now Ive made non-rotating T nuts.
I thought it would be a easy thing to do on a rotary table, not so.
Anyway the jobs done.
Mark

Good work. I need to make up one. My lathe has 2 bolts/nuts in the normal position, but it also has another hole for a bolt at the front of the compound slide. I think it would be a good idea to fit a bolt here, at the rough end of town, although it has never had one since I got the lathe. The bolt hole is just inside the lower ways.

Dean

[jhovel]

I guess you could just turn a full top-hat shaped ring on a lathe, matching the diameters of the circular T-slot. Then drill and tap a heap of holes around it and cut it up into the arc segments required. You'll end up with a good number of spares then.... just sayin' - if you don't want to mess with a rotary table on a mill....

[krisfarm]

It seems like this is a common problem with some lathes, my AL1000D suffered from it, so I made up a solution some years ago along the lines that Joe is suggesting. It has fixed the problem. A few pictures to clarify.
Bob

[jhovel]

That is a brilliant solution!

RayG - could something like that help with your Deckel problem? Or is that solved already?

[Oldneweng]

I agree with Joe. That is brilliant.

I would have made the lower individual pieces bigger tho. My prervious lathe had suffered a crash or 2. One of the T-nuts had cracked the casting above it. I found this when investigating "rocking" of the tool post. I removed the cracked section and had no way to repair this so I "knocked up" a new T-nut (loose description) which was much longer, to straddle the broken out section. I also arranged a central bolt that required the compound to be wound back to allow access with an allen key just to add security.

I thought it was interesting that my current lathe also has an extra bolt position, although not in the middle.

Dean

[krisfarm]

Hi Dean,
When I first ran into this problem with the T-nuts I made up a pair of nuts that were each in two halves split on the diameter, they were around double the length of the original nuts, or as long as possible to fit in the groove. Once I had established this length I removed each set clamped the two halves together and drilled and tapped the threads between the two halves. This arrangement worked better than the original set up but did catch and jam up occasionally, I found that the underneath surface of the shoulder was not machined, just as cast. By reducing the surface area of the nuts by using round ones and increasing the radius on the original nuts and adding the top ring. It eliminated the hang ups.
Bob

[Poloris]

Krisfarm I wish I'd thought of your solution, my T nuts work fine but I can still feel the nuts bump the T nut entry hole as I rotate my topslide.
Whilst making the nuts, each time I changed radius, I had to remove the jig, locate the rotary table centre, refit the jig move the cross feed table to offset the rotary table then relocate the jig before fastening at the new radius and finally cutting. Not hard but too many steps.
I have a complete myford cross-slide in a drawer.
I can make dovetail mount for it and fasten it to the rotary table and add a small milling vice.
I will have to devise a locking mechanism or use the gibs to lock it.
That would give me a easy and measurable way of changing radius whilst making small parts on the rotary table.
Who knows I might even use it.
Mark

[Michael G]

Mark,
I might have this completely backwards, but I can't see why you would need to remove the jig each time you change radius. All the radii should swing from the same centre point I would have thought so all that should be required is to move the table the R/T sits on by the appropriate amount. Putting a cross slide on the R/T won't help as while that will change the position of the work with respect to the centre of the R/T, the important change is to move the centre of the R/T with respect to the cutter.

Michael

[Poloris]

No Michael the jig must be moved on the rotary table each time to change the radius or it will just make the same size circle in a different position.
Instead of finding the centre of the rotary table each time, I could have just put my centre finder in the jig locating hole then moved the cross-slide to the next offset position then repositioned the jig, That would have cut out two steps, but I did not visualise this.
I haven't used the rotary table that much.
Mark

[Oldneweng]

No Michael the jig must be moved on the rotary table each time to change the radius or it will just make the same size circle in a different position.
Instead of finding the centre of the rotary table each time, I could have just put my centre finder in the jig locating hole then moved the cross-slide to the next offset position then repositioned the jig, That would have cut out two steps, but I did not visualise this.
I haven't used the rotary table that much.
Mark

I f you cut the smaller inner radius first, then move the mill table to locate for the outer radius, this will change the radius of the cut.

http://metalworkforums.com/attachment.php?attachmentid=363182&stc=1&thumb=1&d=1467631946

Move the mill table to the right until the cutter lines up with the centre of the rotary table and you will have a cut with zero radius. The radius has changed. I don't understand why you have to go thru all these steps. Am I missing something.


or it will just make the same size circle in a different position.

If you move the mill table the radius will change. How does this make the same size circles?

Dean

[Poloris]

We are going around in circles, no pun.
The radius of the cut will only change if the jig is moved in relation to the centre of rotary table.(bigger or smaller radius)
Moving the mill cross table will only reposition the circle, the same size circle will be cut.

Mark

[Michael G]

Moving the mill cross table will only re-position the circle, the same size circle will be cut.

No. If the jig and work piece stay in the same location on the R/T, by changing the distance between the spindle axis and the R/T axis (wind the table across), a larger radius circle will result. (Think of it this way - if you had a piece of board on your R/T and a pencil in the chuck, if the axis of the spindle and the R/T coincided, you would get a dot on the board. If you cranked the table across say 50mm and then revolved the R/T, you would get a 100mm circle)



The radius of the cut will only change if the jig is moved in relation to the centre of rotary table.(bigger or smaller radius)

Sort of - if the distance between the axis of the R/T and the spindle stays the same, moving the jig will put the same radius on the part but the centres of the radii will not co-incide. If you move the table that the R/T sits on after moving the jig then you may get a larger radius, but not because you have moved the jig.

Michael

[swarfless]

Sorry Mark, my money is on Michael's argument. For my part I cheated & used the adapter plate I made to raise my Chipmaster's topslide to hold its T-bolts & held that on a stub arbor & ground the radii on the T & C grinder. Used M14 socket cap screws as the material, roughed out on the Myford. Piece of cake.

[Oldneweng]

The radius of the cut is "Purely" determined by the distance between the rotary table centre and the cutting edge of the cutting tool.

It does not matter how you change this distance.

Dean

[Poloris]

Yes Oldneweng you are right, and I'm wrong.
I've been over thinking it again.
Mark

[Michael G]

... you are right, and I'm wrong I understand better now how a rotary table is used.

Sometimes understanding relationships between things can be really confusing. I've had a couple of :doh: moments myself.
Michael

[Oldneweng]

Sometimes understanding relationships between things can be really confusing. I've had a couple of :doh: moments myself.
Michael

Really. That has never happened to me.:D

Dean