Re: [CAD_CAM_EDM_DRO] dovetails for cnc

skykotech wrote:

>I am toying with cnc'ing a small hardinge dv-59 lathe. This lathe
>does not have a longitudinal feedscrew so I will have to add a
>leadscrew or ballscrew. The bed is a ~3.5" wide dovetail (60
>degree) way. I want to machine a mating carriage to ride on this
>dovetail.
>

Why on earth would you make a new one? Or, is this a turret lathe
with no carriage?

> I have the correct carbide insert dovetail cutter on
>order, but I am wondering what is the correct way to make the
>dovetails and gib. Does it matter for cnc if I make the gib
>straight instead of tapered? There is not a lot of information on
>why gibs are tapered or how they compare to non-tapered gibs. Also,
>I have been told that you need to taper one of the four dovetails if
>you use a tapered gib. I took off the cross-slide on my 7x12 lathe
>and it just uses a straight dovetail and straight gib. Of course
>this may not be the highest quality thing I could have examined.
>
>

You probably want to hand-scrape the new carriage to match the bed.
Use Canode dye (available from Dapra, as well as scraping handles,
blades and etc.) You might consider the book and/or the video by
Michael Morgan http://www.machinerepair.com/home.html but pay
with a credit card, as he sometimes takes forever to deliver. But, the
books are worth it. (If you ever get a chance to see him work, it
would be worth a few hundred miles drive. I saw him do a lathe bed
at the NAMES show in, umm 2003? 2002? and it was pretty incredible.)

Hand scraping will get a very accurate fit to the shape of the bed.
Make sure you put in some oil grooves to adequately lube the sliding
surfaces.

Or, you could use a castable way liner such as Moglice, sold by Devitt
http://www.moglice.com/newsite/pages/applicpages/rebuildframe.html
I used this on a larger lathe rebuild, had no idea what I was doing, but
it has worked out very well.

Without extensive gear, I think I'd go with a flat gib and a row of
adjusting screws. Making all the tricky angles for a tapered gib could
be complicated.

Jon