Thanks Richard,
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
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-----Original Message-----
From: CAD-CAM-EDM-DRO@groups.io [mailto:CAD-CAM-EDM-
DRO@groups.io] On Behalf Of Richard
Sent: March-02-20 12:07 AM
To: CAD-CAM-EDM-DRO@groups.io
Subject: Re: [CAD-CAM-EDM-DRO] Work Holding
I do not have a problem with your approach. Clamp 4 jaw, turn spigot
(nub), then hold in collet block to drill and bore.
I would superglue a piece of 1/2" aluminum to what will be the bottom
face of your piece in the collet then after clamping the collet block in
the vice place a jack under the aluminum and jack up tight. You can now
drill and bore on through into the aluminum. Jack there for security.
Aluminum so you do not drill jack! After boring I would skim the top
face then turn over remove alu block and skim the other face at the same
height. You could do the same to the sides as it would make the
subsequent holding in the 4 jaw easier. Initially (given that amount of
material) I would make the spigot as long as possible to assist in
holding in the collet, then machine to drawing length last thing. Last
point do you have a 25mm collet? If only a 1" then I would turn to 1"
and at the end of the job turn down to 25mm.
Good luck
Richard
On 01/03/2020 21:02, John Dammeyer wrote:
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
