Making a cup in the end of a bar

[Round in circles]

I have a need to make a shape like an cup or drinking tumbler on the end of a 1 & 1/2 " bar of steel and once made and tested for correctness I'll turn a stem on the bar so it resembles a stemmed wine glass so I can fit the cup in a drill press and cut out zillions of foam circles . The cup's internal dia is 22 mm , OD is 24.5 mm with a depth 11 mm .

I've turned the basic shapes but found it very , " chattery " inside the cup and the finish inside looks like fish scales rubbed up the wrong way. On cutting out a disc the roughness makes it a bit too tight to remove the disc unless I stop the drill and use a needle to pick it out . If it were really smooth I think it will fall out as I raise the cutter
The tool I'm using is an overley long 3 " of ground round 1/2" square bar 1/4 " thick at the round part of the bar , it has a 1/8 th " purpose ground beak that is the cutting part . The boring bar appears to have been hand ground up from an angled left hand high carbon steel cutting tool

I've been using speeds of 500 for the external roughing out & 1270 to give a finish , 500 & 805 for the internal steel removal .

I've tried kissing it on the grind stone to get the cutting edge and angles in a reasonable state.

My questions are these ....

(1)
With the tool post on the right ...work on the left , bar boring the cup out towards the front/saddle of the lathe , I'm working blind ..I can't see the tool tip . Do I invert the tool put it on the back of the tool post at the center height and cut at the back edge /away from the front of the saddle . ( I have a crippling spinal injury that stops me leaning forward to see the tool tip inside the cup ).

(2)
On the tiny beak cutting tip , the actual cutting tip is almost good enough a point to run /turn a fine internal thread . Would my putting a 1/32 flat /slightly radius'd chisel point on the tip make a better less noisy cutter so I can use a few more thou to try and get a better internal finish ?

I feel that once I've ground the " beak ", the boring bar is only going to be fit for scrap quality high carbon hand forged steel as there will not be much of the beak left .

 

[Jim2]

Yeah, you can cut on the far wall up-side down--no problem as long as you can reach. With 22mm ID that would be no problem. Otherwise a mirror can be used as well. Oftentimes, no real good way of seeing in a bore like that w/ tool-post in the way and all.

If you're having trouble with finish, I'd suspect lack of proper clearance on your tool-bit. . . . If the bit is rubbing instead of cutting you're going to have lots of chatter.

My lathe is nowhere near capable of cutting at the speeds that you're at, but that does sound awfully fast unless maybe using carbide? When boring you want to limit your tip radius as boring bars tend to be flexible--though 11mm isn't much depth either. Make sure you're choked up as much as possible to make the most of your set-up.

HTH,

Jim

 

[jererp]

I'd make sure the cutting edge is slightly above center. Part geometry gives you more tool clearance. Also, if possible shorten the boring bar overhang. Turning at a slower RPM may reduce the harmonics of the boring bar.

 

[Boswell]

I'd make sure the cutting edge is slightly above center. Part geometry gives you more tool clearance. Also, if possible shorten the boring bar overhang. Turning at a slower RPM may reduce the harmonics of the boring bar.

while it is not quite your question. If you put a spring inside the "cup" it will compress when you cut the foam and eject the foam when you back away from the foam.

 

[Hawkeye]

Alternatively, you could drill an angled hole or two out through the cup so that a wire or screwdriver can be pushed in and pop the cutting out.

 

[samthedog]

I would just use a small grinder to grind the cup smooth like a toolpost grinder and add a spring as Boswell mentioned. No matter how smooth you make the punch, if the foam is compressable self ejection will not occur. I have seen many presses and punches used in shoe factories that all had to be cleared by hand or a spring.

Paul.

 

[Dave Smith]

drill a hole in the backside and just give a short blast of air to remove it without damage-----Dave

 

[Round in circles]

Thanks for your input guys , I read up about the harmonics earlier today and so used a much slower speed as well as putting the boring bar in upside down to cut on the farthest wall after a gentle regrind , had to pack out the tool post seat to raise it enough to get the cutting edge at centre height as I don't have a nice and handy quick release tool post that I can compensate things with YET! There is sufficient clearance to cut right through the 10 mm thick foam as the recess is 13 mm deep .

The spring ... Having cut about 100 of the foam washers tonight , the OD is almost exactly 40 mm and ideal for my needs I was trying to think of a way to self eject . I don't possess a compressor ,so every washer was cut to almost the half way point on both sides and then hand removed from the sheet of foam every time I'd semi cut 12 holes ...T'was a long laborious task especially in the near frost conditions out in the garage.

In the centre of the cutter I have set a pointed bar to guide the foam under the cutter through the same hole so everything lines up for cutting from both sides.

Now with the spring ejector and a sort of face plate idea I may have it cracked ...what I don't want to do is tear the faces of the foam disks up with the spring as the cup rotates in the drill press.
I did try to simply use the drill press as a stamper/press to cut through the 10 mm thick foam but it will not do it .

Just had a cup of drinking chocolate , as I made it I had an inspiration .:talktogod::roflmao:.

I'll make the cup 2 mm deeper , open up some of the solid body and insert a captive spring operates shuttle with a nice big face to press on the foam and also reposition the guide pin by making it a lot longer and locked in .... almost up in the drill shank of the cutter or maybe use a much thinner bar and actually set it in the 1/2 drill neck
as in this ...


I'll have a play at it tomorrow , once I've put an electric fan heater in the garage as we're forecast snow & a sharp frost tonight .

 

[Dave Smith]

you should have an air compressor to make it quick and easy--I think you are over making a simple punch that should work fast in just one side stroke full cut------working with a plunger and spring is going to make it harder to compress it all while forcing the punch down----I just cut a side slot little over half way through the punch so the punched item can be taken out the side when the second piece pushes it up---I made mine for leather and rubber holes and they work great----I just cut a gas filter in half for two cheap cutters-------Dave

 

[Round in circles]

Dave Smith , do you have to stop the drill press to extract the cutout and or blow it out ?

I considered one of the old hoop and stem type saddle makers leather punches that self eject if you fill the cutter void up by continualy punching things out . I saw a 40 mm one on eBay yesterday morning ..I'm not bidding for it .....when I looked the price was already at £ 49 ( $ 75 USD approx.) aand still four or so days to run

Sadly I dare not have a compressor yet unless I can find a super quiet running one that does not make a hissing sound when using an air blast . For it would give the Witch & Goat next door yet another thing to ***** and whine at alongside me being disabled , no longer fit to work sensibly & getting a government funded Motability car to help get me around .

Her husband " Has to work his fingers to the bone all week & I stay at home living the life of Riley " according to one of her outbursts directed at me and my family .
He works for the government in the driver licensing place here in Swansea and wouldn't know a decent day's work even if it bit him twice in his butt & smacked him between his eyes with a baseball bat , neither would she. :roflmao:

An Eureeka moment ???
I've just had a thunk , if I turn up a cutter like yours but make it a bit longer in the body and in the elongated cut out insert & fix a round bar cut to a wedge to give an automatic ejection slope to eject through the cut slot it may work . I'd like to make about 24 x 14 x 14 of these foam washer inserts ( the amount of material I have)