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| how to accurately mill a rectangle with rounded corners (no cnc) |
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| picclock:
I need to mill a rounded rectangular slot 3.5mm wide x 1.3mm deep in a piece of aluminium. The corner radius is 60mm. I have a rotary table but its the positioning and alignment that's tricky. My mill has DRO's so I'm thinking maybe work out the XY coords. for the curve and advance the table accordingly. Need to do this in the next few days so I have a little thinking time (I need it all .. .). The pro's and cons are these. With the rotary table I can get smooth curves easily, but getting them in the correct place is not so easy. Assuming I cut my 4 curved corners, I can then try to align the work on the table so that the horizontal and vertical cuts seamlessly intersect the quadrants. Aligning the endmill to the centre of the end of the quadrant is likely to be tricky. Using calculated tables will give a more stepped approach, even with a large number of iterations. The potential for errors whilst doing this manually is very high, and I'm not that confident that I can do it 4 times without significant errors. I suspect that it will need at least 100 coords to get the curve to a reasonably smooth profile. Can't think of any other ways at the moment. Jigging the rotary table will get the corners more or less correct, but I need a technique to align the endmill to join up the quadrants. Whichever way I go I will have a couple of practise runs. Any help much appreciated. Best Regards picclock |
| Lew_Merrick_PE:
--- Quote from: picclock on July 19, 2011, 03:41:18 AM ---I need to mill a rounded rectangular slot 3.5mm wide x 1.3mm deep in a piece of aluminium. The corner radius is 60mm. --- End quote --- Pic, Let's try this one again. You need to mill a slot 3.5 mm X 1.3 mm with an R60 mm corner radius? Are you sure that isn't an R0.6 mm? (Understand that I have never once had my fingers go dyslexic on me -- 50,000 times maybe, but never once!) A 60 mm radius is a 120 mm diameter. A 0.6 mm radius is a 1.2 mm diameter. I sure hope that the aluminum is 7075 or 2024 and not 6061 for this as 6061 would be a RPITA to mill with that small an endmill (slot drill). So, if my interpretation is correct, I would start by milling with a (say) ø0.8 mm endmill as short as required to make the full slot depth to make a 3 mm long start and then switch over to a ø1.2 mm endmill to finish it. Both endmills would be as short as possible. Use lots of lubricant/coolant. Keep the air-blast handy to clear the chips out of the slot. Please note my initial question. Something does not sound right in your description. I may well have misinterpreted the question. |
| John Rudd:
Lew, Your reply was exactly my initial thought, hence my reluctance to reply to the question... I think Picclock has got a measurement wrong... Milling the slot to the dimensions stated isnt a problem if you have X/Y dros...Set your initial starting point and then move according to the co-ordinates.. Milling with a .6mm cutter needs a lot of rotational speed......if you can get a cutter that small!! |
| DaveH:
Picclock, Me thinks a little drawing maybe useful. DaveH |
| Jasonb:
I think he wants to mill a slot to form a rectangle with rounded corners, bit like the O ring groove in Robs hit & miss build. So its 4 straignt cuts joined with a quater circle of 60mm radius. Its a case of very carefully locating the centre of teh 4 corners onto teh rotary table axis and then joining them with 4 staright grooves, just a lot of carefull setting up using edge finders and dti. J |
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