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开云体育I think this may be the best forum to ask this question as it's less about CNC machining and more about general machining. ? The photo is of the ACME bronze nut on my X axis mill table.? Clearly a casting with the numb turned to 25mm and an almost press fit into the X axis location.? ? I think the way it was made was that it was held in a 4 jaw chuck and turned to be that exact 25mm.? Then perhaps held in a collet chuck on the mill and bored and tapped?? And the backlash on this little beast is almost 0.025" ? So I'd like to reproduce it but with an adjustable backlash remover.? Something like the attached CAD drawing. ? I don't want to spend over $100 on a 1" x 5 TPI ACME tap.? Likely a boring tool with the right profile can be used on the with the advantage that I can have the lead screw out of the mill for trial fits as I sneak up to the dimension.? ? Is first turning the nub to 25mm while the replacement slightly larger bronze piece is held in the 4 jaw the right way to go?? I want the horizontal hole for the thread to be exactly perpendicular and on center to the nub.? Is a 5C collet holder accurate enough on the mill so I can drill and then bore to the thread size??? ? I can see at the same time using an end mill to flatten the drilled surface so that it's placed against the back of the 4 Jaw and then the 4 jaw is adjusted until the bored hole indicates that it's on center. ? Or should the ACME threaded hole be drilled and tapped first and then somehow held so that the 25mm numb is turned?? The centerline of the threaded hole has to be exactly 19.80mm (although I might have measured wrong and it's 20mm since the rough dimensions of the casting are 40mm x40mm. ? If I get that height wrong of course the leadscrew will be too low relative to the bearings on the end of the X axis table. ? Looking for suggestions and ideas. ? John ? ? ? |
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Thanks Richard,
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One other idea I have that certainly didn't come with the user manual is the distance from the top of the X Table to the milled flat area by the 25mm hole. So I have to take the lead screw out again, slide the table over far enough so that I can come up with a measurement that is accurate to at least 0.0005". Once I have that I could then recast and re-machine the end plates with the entire lead screw moved up so there's enough clearance for a ball nut assembly. Right now there isn't. The existing replacement end plates were matched to the old ones that used bronze bushings where the new ones use a double set of angular contact bearings at the motor end and a regular ball bearing at the RHS where the power feed was. I think the original distance to the leadscrew was based on the mounting holes in the power feed end plate which is a die casting and there's not a lot of latitude for up/down position. However there is lots of room above the lead screw so going up 10mm to make room for a ball nut would not be an issue. This doesn't change the need for a mounting bracket that places the ball nut face at right angles to the table surface and a ball nut mount will need to be precise compared to a sloppy fitting ACME nut. Oh and the really most annoying part of this conversion? The holes drilled and tapped into the end the table are not precisely positioned. Especially the RHS where the power feed was. It was mounted so it was twisted by about 3 degrees. Once they had it aligned they drilled for taper pins. On the new motor and bearing mount castings I can't use the taper pin holes. They aren't a proper distance from any reference surface either. Sigh... John -----Original Message----- |
