Supporting > Tooling & Machines
Yet another Quorn
Charles Lamont:
Well, you certainly did not want that Wheelhead Collar going walkies! Mine was the next to get some attention.
The first photo shows getting an initial datum surface, square to the body in two planes. Second photo, roughing the other end parallel to the first. After measuring up, both ends were finished to size, along with the little pads for the tilt adjusting screws. Next, it is set up square two ways for marking the hole positions for the clamp pad and the mounting pivots for the Wheelhead Bracket.
The fourth photo shows the casting packed up to centre height and set square with reference to the angle plate. (Setting square to the spindle means doing just that - with a turn round test. Traversing the cross slide past a stationary DTI tells you if the angle plate is parallel to the cross slide, but not necessarily that it is square to the spindle. Cross slides are mostly set on a new machine to turn a face slightly concave.) That hole looks as though it is too close to the bore. That is because the casting is intended to be slit through for clamping, but with pad clamps the hole needs to be closer in. The casting will be cosmetically dressed to suit. The hole may also look too close in because it is. Subsequent measurement shows it is 0.048" too close. Expletives.
I don't know how that happened, but it is going to have to be remedied. I don't propose to scrap it. Firstly, setting it up again is easy. Sat on the same packers, it can be lined up accurately with a 1/2" bar in the chuck passed through the hole, and can then be offset to get the hole in the right place using the cross slide dial. Boring bigger in the right place and fitting a sleeve would leave the casting too thin. What I mean to do is make an iron plug to go in the hole (to be fitted after setting up).
It will be no good pressing it in, because re-making the hole will leave the plug as just a thin crescent on the inner side. It would probably fall out. So, it will have to be glued in. But what with? Because the clamping pressure pushes outwards, fortunately the plug will not actually be subject to any load. Options I am considering are Loctite, JB Weld, and Araldite. Of these, I think Loctite in this situation may be a bit brittle and liable to chip in re-boring, and I think JB Weld may be too viscous to coat a thin joint that has to be assembled by sliding. I am thinking Araldite may be the best bet, as it will make a fairly thin joint and machines OK, but I would welcome thoughts.
Chipswitheverything:
Well, I must say that when I looked again at the forest of clamps that I'd used to hold down the Wh. Head casting, it did strike me as a bit frenzied : but I think that the idea had been to get a sure grip for the boring operation while not using too much clamping force at any individual point , so that the bore remained round rather than being slightly ovalized when the job was released. Probably!
Bit of a bind about the quite small discrepancy in the plug position, but I wonder, could you bore with the brass plug inserted in the present position, and make good with some minor dressing back of the plugs where they contact, and a similar small necking in diameter of the locking bolt to clear the column ? Dave
Del_61:
I use pieces of card or thick paper interposed between clamps, castings and the machine table. This provides better grip without having to result in overtightening the clamp or studs.
Regards
Derek
Charles Lamont:
Dave and Derek, thanks for your comments. I agree on being careful about clamping pressure. I have a pack of redundant business cards that I use a lot for clamping, often as protection as well as for improved holding, though not when working to a dimension above the boring table.
I have been on Quorn Owners on Groups.io and its previous incarnations going way back, but there does not seem to be much traffic there of interest these days.
I don't know about making the belt joint. Are you using a guide such as a V-block for bringing the hot ends together? I am planning to use a little Poly-V belt on mine, H-section, 3-rib.
I have had a think about using the Wheelhead Collar casting as is, with a necked-down clamping bolt. I think it would work, but I am not sure I would feel happy with my workmanship. Plugging and reboring will be a more 'interesting' exercise anyway.
Charles Lamont:
To solve the problem with the wrongly positioned hole in the Wheelhead Collar, the first job was to make a plug to fill the hole, with a two thou radial clearance for adhesive. I could perhaps have used steel, but chose iron for the bodge to be as near as possible.
Next, I reset the job on the boring table using the preserved packer stacks and recreating the position with a silver steel bar through the hole. Once clamped, the cross-slide could be moved the necessary 0.048" and locked at the corrected hole position. With that done, I could Araldite the plug in place. As the shop was pretty cold I let it cure for several days before re-boring the hole.
With the same set-up and the offset measured on the cross-slide dial, I counterbored and centre drilled the pivot hole. As originally planned, I then turned the job round, reset with the 1/2" bar, wound the cross-slide the other way and put the matching pivot hole in the other side.
The last, not very good photo, shows the glue line round the remaining crescent of the plug, appearing wider through the hole as it and the 0.002 thick cylinder of glue are tangential.
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