How do I do this?

[daz]

I need to make the part in the drawing below.

I can do the turning etc, but the one thing I am struggling with is the recess. I don't have a tool small enough so I tried to make one last night out of a piece of hardened steel. It worked ok for a short time but then started chattering like crazy and snapped, unfortunately ruining the piece by ripping through the outer wall.
Can anyone show me the way please?

TIA

Daz

[jim]

end mill and rotary table?

[daz]

I don't have a rotary table unfortunately
Sorry I should really have said what I have at my disposal, might have made it a bit easier. I have a small lathe and an eagle 30 milling machine. I look forward to the day I can justify a rotary table for it 

cheers
daz

[Fergus OMore]

Daz,
         What you need- and I mean NEED is a copy of George Thomas's Model Engineers Workshop Manual. If you can rustle up more cash, get a copy of Sparey's The Amateurs Lathe and perhaps GHT's Workshop Techniques.

You desperately need the ability to make good boring tools and understand how they work. Despite ALL this prattle about carbide 'doo dahs' bought from a shop, there is NO substitute for a set of little tools made up on a home grinder out of- old hexagon keys or bike spokes or  something 'equally exotic'

Where you probably went wrong is not giving enough side relief on your now broken tool which jammed against the outside bit of the cut in the hustle bustle of swarf and crap. Again, you might have had the wrong tool height- which alters the cutting geometry of your tool.

Having written all this, might I remind you that you have more than most 'big' items but now need to make those nice little items that do the work.

George Thomas rightly mentioned that 'if you didn't have the proper little bit at the cutting end'-- well, read on.

Let us know if I have it right, please! You'll enjoy the progress.

[daz]

I think you could be right about the side relief, it was fine when taking small side cuts off from the first groove I cut but really noisy when doing a cut the full width of the tool if you see what I mean. Thanks for that, I will go and have a look for the books you recommended and some more reading.

thanks
daz

[Fergus OMore]

Daz,
           You should draw the annullar ring to full size and draw your tool cutting into the ring. I'm guessing that you need a lot of facets in your cutting tool rather than, I suspect, the normal Two. Again, you want to grind a little waist- like a golf club end.
It's got to be 'titchy'.

Hope this helps

[loply]

Drawing indicates the recess is just for weight purposes, presumeably therefore is dimensionally flexible.

Consider using a holesaw? They work surprisingly well without the pilot drill installed...

[Fergus OMore]

I was also suggesting a 'hole saw' but with one Granny's  tooth.
Aged and ageless stuff!

[BillTodd]

How about a broaching cutter (like a posh hole saw) it'll give better finish and will probably be quicker of it's a production job.

http://www.lawson-his.co.uk/scripts/products.php?cat=Blue%20Up%20To%2050mm%20Dia%20%28L%3D25mm%29

[Fergus OMore]

Actually,I sent Daz a picture of how GHT made a small boring tool.

I made mine from a bit( pun intended) of HSS round and waisted ( not wasted it) to make a Harry Lauder stick or golf club.

As I said to Daz, it's the lirttle bit at the end what does the job.

What we( well, most of you) have gone so far along a branch that you have forgotten that round tool steel  can be made to follow all sorts shapes.
If push comes to shove, a round bit of hss can be a broken bit of a drill. GHT used broken little centre drills!

I'll get me coat!!!!!!!!

Bye

[Doc]

That cut would be what is called trepaning. Here is a link to some info on grinding up a tool for the job. Trepanning Tool

[sbwhart]

Make it in two peices and press or glue or solder together.

Stew

[Doc]

Here is a picture of a very similar part being trepaned with a hand ground tool.




And finished parts.

[daz]

I did try making up another tool to try and see where I went wrong, and as Fergus OMore pointed out I didn't have anywhere near enough relief. The second one worked much better and got the job done. Thanks again for all the replies guys, all stored away in some dark recess of my mind for later use
One thing I am still questioning about the part is why bother leaving all that material on? The part is there to connect onto a con rod and to seal the displacer piston, why not cut all that material away leaving just a shoulder around 3/16" long by whatever diameter is needed for a press fit, could even use a bit of loctite if required??? That would surely cut down on the weight even more.
mmmhhhhh. I think I am going to have to make another one now just to see if there is any difference!


cheers
daz

[winklmj]

Since it's not a precision cut--make one of these:



Turned on the lathe and the teeth were cut with a Dremel tool.

I used that to cut the spring seat in this part:

[Fergus OMore]

I did try making up another tool to try and see where I went wrong, and as Fergus OMore pointed out I didn't have anywhere near enough relief. The second one worked much better and got the job done.daz

Great news,eh?

Ah well, you are now ready to graduate to trepanning the labyrinth seals on  Professor Dennis H Chaddock's Quorn tool and cutter grinder's high speed spindle.

Winks quietly and dozes again in his wheelchair.

'Fergus'