Re: [CAD_CAM_EDM_DRO] Re: Cost estimate for machining of acme screws

Drigotti wrote:

> I was wondering if anyone can give me an idea of the cost to have 3/8" acme
> screws cut and machined down to 1/4" on one end.
>
> Just wondering what the going rate would be?
>

JanRwl wrote:

> Here (Houston), the smaller shops charge $100 and more per hour, and
> most have a "$100 minimum".
> I have done "[ACME-]screw ends" so they would properly fit ball-bearings, and
> that takes some time! You not only have to use a brass sleeve over the
> screw, where the chuck "bites down" on the O.D. thereof, and "fit" that,
> before use, etc., but you have to SLOW DOWN when you approach the final
> shaft-diameter, and "mike often", to make sure you don't "go a thousandth
> under", etc. This takes MUCH more time than just whacking off 1/2" of
> diameter of the end of a length of round bar-stock!

Tom Murray wrote:

> --- In CAD_CAM_EDM_DRO@y..., JanRwl> wrote:
> >It will very likely cost you MORE to have "kids" do
> >the job that it will if you have a PROFESSIONAL machinist
> >with a reputation for fine work do it RIGHT the
> >first (and ONLY!) time!
>
> I have to agree with the above sentiment. I willing to spend enough
> to cover the cost of a professional job. Just wondering what the
> going rate would be?

It is for these reasons and more, that I decided someone needed to
provide this service. I initially played around with these smaller
diameters, but they do lead to some very minature machines.

For example, 3/8" acme can indeed be turned down to 1/4" dia
(the minor dia varies from 0.2632" up to 0.2817" ), but as 3/8"
comes (usually) as 12 TPI, thats not as nice as 10 TPI.

Hence for the smaller stuff, I use 1/2" acme which is 10 TPI, and
can be turned down to 0.3595" - 0.3800" minor dia range, which might
be under .375" sometimes, so I turn it down to 9mm (0.3543") for
which bearings are available.

9mm seems quite a bit more robust than the 1/4" dia (it has twice
the metal area) and as I mentioned the 10 TPI is nice to work with.

While I'm at it, I'll describe the 3/4" and 1" dia too...

The 3/4" dia (6 TPI) has a root dia .5371" - .5633" and so I usually
turn it down to .500"

The 1" dia (5 TPI) has a root dia .7509" - .9900" and so it usually
gets turned down to .750"

Of course most of my leadscrew work is in this 1" dia * 5 TPI style
(see my webpage for a description of the leadscrew kits premachined
with bearings and motor couplers).

However, I've had lots of requests for the 1/2" dia * 10 TPI and so
I'm thinking of stocking that too (to make available 1/2" leadscrew kits).

If people email me, I'll get an idea of the popularity of it and maybe
proceed with it if theres enough interest. This size would be good
for Dave Rigotti's nice little cnc gantry router at http://www.hobbycnc.com/

Dave, if you think its a good idea, send me the dimensions your router
requires, and I'll make up kits for you & your builders.

Remember to use a nut with at least 3:1 length:dia ratio to more or
less eliminate backlash, without having to use friction causing compression
nuts. Actually for this small dia, 4:1 would be even better.

regards
Doug Fortune
http://www.cncKITS.com