Rings? Sorted!!

[BK]

I need to cut 8 rings 3 - 3/4" OD from 1.25mm black plate, the internal is OK I have a 3" hole saw (my biggest).
I should be able to hold the plate in the lathe before I cut the centre out, but I'm unsure of the best way to do this.

[sbwhart]

Hi BK

First thing is don't drill the hole first if you have you've made thing difficult for your self.

Starting again the way to do it is to friction turn the OD:- roughly cut the OD into a circle with a saw or by what ever:- Put a big centre roughly in the middle, put a dollop of masking tape on the back of the blank, then with a stub of material held flush to the jaws of the chuck trap the work with a running centre up against the jaws, with you lathe in the slowest speed you have nibble the disc into a circle, when this is done drill the hole in the midle.

A bit like this





Hope this helps

Stew

[John Hill]

You need a trepanning tool, which not hard to grind, for the lathe but you also have to arrange a holding system so that your ring can not fall free when it is cut out.  If it falls free it will likely be looped around your cutting tool and will get jammed by bits of the whirling chuck or attachments on your face plate producing a nice metal pretzel and in my case a barely avoided laundry emergency.

What I did when making gimbal rings for my gyroscope was make a wooden disc to mount on the face plate. I drilled a hole near each corner of each piece of steel (square of 1/4" mild steel) and mounted each piece to the faceplate by bolting the square to the wooden disc.  Then I used the lathe to drill a hole in each plate and passed a threaded rod through the spindle to lock the centre of the plate to the face plate.

Then I made the first cut using my trepanning tool, I cut the inner cut first but I think you could do either.  That cut left me with two pieces on the face plate, the inner round bit and the outer square piece with a big hole in it.  There was a gap between the two pieces left by the width of the trepanning tool and  I put a number of wood screws in this gap then when I made the next cut the wood screws held the cut off ring to the face plate.

There is probably an easier way to do it but that is what I did after having a tangle with my first attempt.

John

[BK]

OK John, who and what is a trepanning tool?? or is it a Kiwi term for something I already know about??? 
The inner circle I'm not worried about, the outer is the pain.
Stew, some food for thought in your reply, thanks.

[zeroaxe]

For a lathe, this is a trepanning tool:




And for a drill/mill, this is your ticket:

[BK]

So it's like a parting tool, only 90 degrees different ?? I hate parting tools, except in brass.

[Darren]

Click here and scroll down a bit, this is one I made in SS for a bearing

http://madmodder.net/index.php?topic=2632.0

[John Stevenson]

Do it all in one go.
Screw a piece of fly or MDF onto your faceplate.
Cut the steel out as squares, drill a hole in each corner and screw to the mdf of ply.
Use a trepanning tool as shown, mine isn't as fancy it just a parting off tool with more side rake for clearance.
Do the inner hole first, then move to the outer, don't worry about going all the way thru as you can pop the bit out and clean up with a file.
If you do go all the way thru no matter it's only into a piece of sacrificial ply, in fact I have one face plat that has ply on it all the while for such jobs as this.

Far quicker than hole saws, neater and they are concentric, 1.25mm thick is a doddle.


John S.

[Darren]

Which reminds me that I need to make a fixture plate for my RT.... 

Thanks John, I've struggled too long without one ....

[John Hill]

Do it all in one go.
Screw a piece of fly or MDF onto your faceplate.
Cut the steel out as squares, drill a hole in each corner and screw to the mdf of ply.
Use a trepanning tool as shown, mine isn't as fancy it just a parting off tool with more side rake for clearance.
Do the inner hole first, then move to the outer, don't worry about going all the way thru as you can pop the bit out and clean up with a file.
If you do go all the way thru no matter it's only into a piece of sacrificial ply, in fact I have one face plat that has ply on it all the while for such jobs as this.

Far quicker than hole saws, neater and they are concentric, 1.25mm thick is a doddle.


John S.

I did that Sir John but when I cut the first ring it fell off and got tangled in the works thats why I now secure the ring with wood screws.

[BK]

Thanks for all the input.
I sorta combined a few ideas of mine and your advice.
First I made a small face plate to hold in the 3 jaw, it's rough but true, and I marked #1 jaw position on the shaft.



Then a block of pine, the work piece and a largish washer.



I put my cross slide stop on and set it to the diameter I needed.



I then attacked it with this little tool, which I seem to use a lot.



That worked well and I soon had a nice circle.I drilled 2 more holes and bolted the lot together.(and forgot to take a photo ) I could then remove the centre bolt and finish the job with my holesaw.


Now a bit of a rub on the wire wheel and I have 1 ring, 7 to go.




Thanks.

[sbwhart]

 

Well sorted

Nice bit of work

Stew

[Dean W]

That's one skinned cat.
Good advise in this thread.

Dean

[Brass_Machine]

Interesting technique! great results.. gonna file this one for future use!

Thanks
Eric