Howard Lewis | 28/09/2021 11:33:54 |
7227 forum posts 21 photos | 50 mm radius on a 25 mm bar sounds like a job for a radius turning tool Either a special just for this job or ma more sophisticated one for other, later, jobs. At a pinch, maybe a boring head mounted on the toolpost, so that it can rotate about its axis, might suffice. (Making a tool, to make a tool, to do a job! ) More ways of skinning a cat, (Not that I am suggesting making a tool for skinning cats. mFirst objection would mbe from ours! ) Howard |
JasonB | 28/09/2021 12:12:18 |
![]() 25215 forum posts 3105 photos 1 articles | It's not on the end of a 25mm bar, look at the images posted. Being quite a thin item if held in a chuck most ball turning tools will foul the chuck |
Howard Lewis | 28/09/2021 13:25:32 |
7227 forum posts 21 photos | Misread the bit about 25 mm diameter. Approaching the problem from another point, make up a concave form tool, run slow and feed very gently along the lathe axis? If you really fancy your chances grind from a 1/2" HSS toolbit! Put some gauge plate, off set in the 4 jaw and carefully turn a concave to make the form tool. Harden / temper as you see fit. Having no clearance the tool would need to be mounted at angle to provide a clearance angle.. For brass, with care, and only one or two to make, you might even get away as is. Howard |
Dr_GMJN | 28/09/2021 14:20:42 |
![]() 1602 forum posts | I didn't buy castings for these end caps, I got some cast iron bar, and will make them from that. I'm going to go for an arc, not an ellipse, because I think the apex looks more defined like that (rather than a bit flat if I use an ellipse). I'm also going to make the apex of the dome project about 1 mm from the bolt face rather than having it flush (as per instructions), again to make the form a bit more defined. If it looks wrong I'll just try again with different settings. |
JasonB | 28/09/2021 14:28:50 |
![]() 25215 forum posts 3105 photos 1 articles | If it's of use this is the profile I drew for the Victoria, radius and protruding |
Dr_GMJN | 28/09/2021 22:11:25 |
![]() 1602 forum posts |
Thanks Jason, I drew something out on CAD earlier, I think it will be OK. Just have to work out the co-ordinates. I think 25 increments of 0.020” on the cross slide should be good, using a 0.8 tip radius tool. Might need back-gear for this one:
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JasonB | 29/09/2021 07:07:43 |
![]() 25215 forum posts 3105 photos 1 articles | The 2.6mm will be OK and still likely to be more than the valve chest cover with it's recessed surface Make sure your DCMT insert won't rub it's edge to start with. You will probably have to start from the outside and work inwards as the tool will rub on the smaller diameters if working outwards. I'd be inclined to rotate the toolpost further so that the edge of the tip nearest you is parallel of just beyond the axis of the lathe, you can then hold something against the edge of the cover and touch the tip against that as you wind the cross slide towards you and as the OD is known you can move 7.5mm in to the first cut Edited By JasonB on 29/09/2021 07:35:29 |
Dr_GMJN | 29/09/2021 13:26:16 |
![]() 1602 forum posts | Thanks Jason. I might turn the tip as you say, and might even draw out a starting geometry that I can rough machine out, to make sure the edges don’t rub. I guess you can see where the cutting edges end by looking carefully at the tip? |
JasonB | 29/09/2021 15:03:52 |
![]() 25215 forum posts 3105 photos 1 articles | Looks like you may just have enough clearance |
Dr_GMJN | 29/09/2021 17:01:21 |
![]() 1602 forum posts | Ah, I misunderstood - tool rubbing on its flank, on the ‘I/d’ of the step? Do DCMT inserts have a standard flank angle (to stop rubbing) that you’ve modelled? Thanks. |
JasonB | 29/09/2021 17:28:47 |
![]() 25215 forum posts 3105 photos 1 articles | Yes, the C in dCmt signifies the angle which is 7degrees and by far the most common though others are available. This is why you see the insert boring bars tilting the insert at an angle so the side does not rub in a small bore. |
Dr_GMJN | 04/10/2021 22:17:49 |
![]() 1602 forum posts | Just to wrap the thread up, I used the co-ordinate method. I used the side of the insert touched on the side of the blank cap, and the tip touched on the PCD face to get datums for everything: Thanks everyone for the advice. Job done with your help - again. Edited By Dr_GMJN on 04/10/2021 22:20:01 |
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