Re: [CAD_CAM_EDM_DRO] Re: re:Lathe Rack & pinion.(cnc lathe)

Arrrr... I have been, and seen, so to speak..

The lead screw does come out, but by a rather non conventional method. Mark
and I were looking at it in the clear light of day (well, it was actually
dark outside, but it's the expression that counts...)

We were looking at the headstock end and I mentioned that it was exactly
like a boxford just bigger, accept it didn't have a shear-pin for when you
jam the carriage into the chuck like we used to at school... Mark says
"Yeah, it does, it's just inside the gearbox". the shear-pin and coupler
are on the gearbox side of the plate and bush it disappears through. Whilst
lying on my back and peering into the bottom of the threading gearbox
through a hole in the coolant tray which I think might double as the drain,
I knocked out the shear pin with a punch and that gives the screw enough
travel left to disengage from the right hand end bush.

You then pull it out to the right end with the carriage hard up against the
chuck (where it got stuck on the chuck, hence the reason you had to pull the
screw out I imagine :-) ) so it doesn't bind in the split nut etc.

We didn't go as far as to take it out, as there was no point, but if the
need ever arises. More importantly Mark will know not to use a 8mm punch to
take out the 8mm pin... It takes just as long to get the punch out as it
did to get it in.. (oops).

Anyway, he's quite a bit keener than I thought to make this thing work.
He's going to order a ball screw and flanges from the local SKF folks
tomorrow, and machine up his own mounts to fit standard SKF thrust bearing
plates. I'll take some photos when there is something to look at and post
them to the files area. The ballscrew is going to live on the back of the
bed as Mariano suggested, and there is enough overhang on the carriage to
just bolt up the nut to a right angle bracket of some sort.

This conversion is a bit outside the league of a lot of us here me thinks, I
get the feeling that this will see the thick side of $30,000 for the
conversion, not including the control. He's got glossies for a Fanuc or
some sort sitting on his desk, I only got as far as the prices for the huge
ballscrew before I was suffering from expense overload. I originally
thought he was "just curious" about how I converted the wee lathe, fact is
he brought the big lathe with the idea of converting it from the start, and
had already researched the cost of ballscrews, servos, controllers etc.

His logic on the retrofit is that another CNC centre to rough out the
castings they use would cost $160,000 new, and will only give 5 years
service before it needs an overhaul. This lathe cost $12,000, plus $2000 to
get it moved and add a new concrete pad in the shop, which would be needed
for a new machine anyway. The conversion will cost $30,000 and it'll last
just as long, if not longer as the machine itself is built like the
proverbial shithouse compared to a modern lathe. I suspect tolerances are
fairly loose on the work he does, so the lack of precision in the bedways
etc probably isn't an issue.

And to cap it all off, I didn't manage to get him on the consultancy fees...
Was worth a try, but he's gone way past the point I can offer advice. He
was just asking me for an opinion as a "crap filter" to make sure he wasn't
doing something silly... As it turns out someone else beat me to it with
the suggestion of putting the screw along the rear, so I can't even get any
brownie points for that, although I might use that tip on my own lathe if I
convert it...

Cheers, Chris.

* Design engineer, Assembly worker, Cleaner.
* Ohmark Electronics. PO Box 5302, Christchurch, New Zealand.
* http://www.ohmark.co.nz

----- Original Message -----
From: Smoke <Smoke@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Monday, November 13, 2000 7:08 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: re:Lathe Rack & pinion.(cnc lathe)


> You could alter the lead screw where in enters the gear box. The way to
do
> this is to cut in in two and rejoin the pieces with a coupling and a
"shear"
> pin. That's the way the feed screw on my lathe is set up. I'd think the
> lead screw would work that way two. Of course I'd use a solid steel pin
> here instead of the aluminum pin on my feed shaft.
>
> Smoke
>
> -----Original Message-----
> From: Chris Hellyar <chris@...>
> To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
> Date: Sunday, November 12, 2000 10:23 PM
> Subject: Re: [CAD_CAM_EDM_DRO] Re: re:Lathe Rack & pinion.(cnc lathe)
>
>
> >Hurro...
> >
> >> manual lathe! Does your "customer" require you to keep all
> >> the "manual" stuff? Or does he/she want a CNC lathe?(with manual
> >
> >? Customer..
> >
> >Now that's an idea, charge him for "consultancy" and then use the money
to
> >buy myself a real CNC lathe... :-). at $50 and hour that'll take, um,
> ages.
> >This is a friend from my old work, he's just brought the lathe from a
> >machine shop that replaced it's heavy iron with CNC gear. He saw my baby
> >lathe cutting some prop adaptors a month or two ago, and has decided he'd
> >like to try the same thing on a larger scale.
> >
> >> IMO, You will spend much more in time to "keep everything as it is,
> >> Just add a little CNC please" than to just CNC the lathe!
> >
> >I'd agree, but I think he wants to keep the fully manual option
available.
> >There is already a decent sized CNC machine in the shop so I suspect this
> is
> >more of an experiment than anything else. Although he's just got a quote
> >for the 3phase AC servos, $13,000 with amps... I suspect he has much
> deeper
> >pockets than me, and I think that's just about what he paid for the whole
> >lathe as well.
> >
> >> P.S. I have a love for old tools, so if its a "nice one", I'd re-
> >> think the whole thing! And just leave it manual :-)
> >
> >It's big, ugly and chinese. And we're not talking nice chinese either,
> it's
> >from the early 80's before the cheap import lathes got their quality
> >problems sorted out. It looks like a scaled up version of the old
boxfords
> >they used to use in schools here in NZ. Even though it was made in 1981
> >(according to the serial # plate) it looks like it leapt right out of a
> WWII
> >manufacturing plant.
> >
> >> P.S.S. If you have room you "could" clamp or thread a timing belt
> >> pulley on the far end of the existing L/S. You said the L/S appeared
> >> cast-in-place? Not likely, IMO, but if so you could make/use
> >
> >Not really cast in place..
> >
> >The right end (free end) sits in a bush in the casting with an Oil bell.
> >The driven end is captive in the gear housing. To remove it you'd have
to
> >remove the gear housing, as the right end mount is part of the main bed
> >casting, which is a right pain. taking the gearbox off looks like a
major,
> >and unless there is a hidden join somewhere it is a huge bit of metal,
> >probably the thick side of 300-400kg of cast iron. Did I mention that
this
> >lathe is not small? It would probably swing 800mm over the bed, and
about
> >3m between centres. Mike makes big pumps, of the sewerage variety.
Major
> >heavy metal work.
> >
> >> a "split" timing belt pulley, and just drive the existing L/S. You
> >> said it was a tight fit with the half-nuts :-) Disengage the pinion
> >
> >I think most of the friction in the lead is due to the the interrupted
> >thread and a massively worn nut.. I'd not trust it past threading type
> revs
> >anyway, it's long, and doesn't look that rigid, I'd think it'd whip quite
> >badly if a rapid traverse was asked of it.
> >
> >Anyway, I'm going over there after tea to see if the rear side ball screw
> is
> >an option, then I'll also see about my consultancy fees :-).
> >
> >Cheers, Chris.
> >
> >* Design engineer, Assembly worker, Cleaner.
> >* Ohmark Electronics. PO Box 5302, Christchurch, New Zealand.
> >* http://www.ohmark.co.nz
> >
> >
> >
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