Re: Spindle motor drive belts MAXNC 10 UPDATE

Hans,

Will have to take some more pics, but I've worked through that one as
well. First I went to 16 pitch acme screws. Reasoning was that since the
torque curve on a stepper falls off as rpm rises, I could get the same
traverse rates at a higher developed torque. No, I don't have any
numbers to back that up, just seat-of-my-pants guessing. It does work
and I can live with the couple tenths of theoretical resolution I've
lost.

First try for nuts was to cast nuts into brass sleeves using Moglice, a
castable bearing resin. This worked ok, but over the length I did it
even the smallest lead variation caused binding.
Next I bought acme bronze nuts and machined them such that they were
keyed into a slot machined at either end of the leadscrew holes. One nut
was fixed, the other adjustable. Used Vibratite on the adjusting screws
to hold. Now I could adjust backlash, but lead errors still caused
problems if I tried to take out all backlash.

Last solution was to pop for self adjusting nuts. I used Ball Screws and
Acutators ActiveCam nuts. These thread into 1/4" thick aluminum plates
that bolt to the saddle outside where the original nuts were. I can keep
backlash around .0005 or so and this has solved the problem with lead
error since both halves of the nut are so close together.

If I have time I'll take some pics this weekend and post the links.
Someday I'll do a proper web page detailing my mods....

Jon

btw, a quickie fix for the nuts is 3/8 brass drilled and tapped 1/4-20
and long enough to stick out from the saddle. Cross slit, deburr, and
use a shaft collar clamp to squeeze together.
You would probably have to machine the collar back some to clear the
slides. This is crude, but unlike the MAX setup, it won't spring open
and unlike my opposed bronze nuts, you can get a much finer control on
the backlash adjustment.


hansw wrote:

>
> From: hansw <hansw@...>
>
> Hi Dan,
> Lots and lots of backlash, new ot of the box it does OK, but soon the
> nuts start to wear and have to be squeezed back together ! more
> crap...!.... The figure " .000125 resolution" would I expect be defended
> with the numbers. The lead screw ( looks like threaded stock I'd buy at
> my local hardware store ! ) and the 200 step motors running half step
> mode the figures say the "resolution" can do that... but not the
> "repeatability" They do have an anti-backlash version, or retro-fit for
> $250.-.... I don't have it... and after this fiasco I will not bother...
>
> IMHO they have the basis for a good product, but need to take lessons in
> customers relations, hiding behind your 90 day warranty has expired is
> no solution for any customer...
>
> However I still like the blue aluminum metal work !!!!!!
>
> Hans Wedemeyer
>
> Dan Mauch wrote:
>
> > BTW Maxnc says their system has .000125 resolution. I know this isn't
> > true
> > becuase they must have a lot of backlash in the leadscrews. How much
> > backlash does your machine have?
> > Dan
> > -----Original Message-----
> > From: hansw <hansw@...>
> > To: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
> > Date: Thursday, November 04, 1999 6:43 PM
> > Subject: Re: [CAD_CAM_EDM_DRO] Spindle motor drive belts MAXNC 10
> > UPDATE
> >
> >
> > >From: hansw <hansw@...>
> > >
> > >Jon,
> > >Thanks for the detailed reply. I looked at your picture, it looks a
> > lot
> > >sturdier than the crap MAXNC puts out.
> > >The guy had the nerve to tell me " we designed it to be flexible"
> > ...I
> > >also notice the carcass of the MAXNC electronics hanging on the back
> > of
> > >the mill.... I purchased a complete MAXNC -10 because I needed a
> > mill, I
> > >did not want to build one....
> > >What kind of electronics are you using to drive the motors ?
> > >
> > >Well I'm in the middle of making a new motor mount. it will be a four
> > >point mount and will allow full adjustment... I'll post the results
> > at
> > >my web site when I done...
> > >
> > >Sure it's a deal, and now that I've re-built over half of it, I
> > regret
> > >not doing it from the beginning, the regrets are about $500.- worth
> > of
> > >motors and electronics and software.. I ordered 70oz-in motors and
> > >realized after a while that they could not be that powerful. My
> > tests, (
> > >see my web site how I do it ) tested the so called 70oz-in motors at
> > >42oz-in..... When I asked to see the manufacturers data sheet on the
> > >motor I was told it was not available and I could get a refund...
> > I'll
> > >keep the motors as a reminder that I should not be so dumb fat and
> > happy
> > >with everything that's fed to me in brochures... I'm not flaming
> > anyone.
> > >I'm just stating the plain honest facts...
> > >
> > >Would I buy a MAXNC again.... Well no... I do learn from my
> > mistakes...
> > >would I recommend it to anyone... Well NO...
> > >
> > >Jon, I appreciate the help and all the feed back, hope I can repay
> > some
> > >day...
> > >
> > >regards
> > >Hans Wedemeyer
> > >
> > >
> > >Jon Anderson wrote:
> > >
> > >> Hans,
> > >>
> > >> First mod I made to my MAX was to toss the spindle motor into the
> > >> spare
> > >> parts bin. I fitted a Sherline DC motor and control. It's a tight
> > fit
> > >> betwen the Z stepper motor and the spindle.
> > >> Here's a link to a pic of mine
> > >>
> > >> http://www.prototype-design.com/images/Shermax1.jpg
> > >>
> > >> You can see here the adapter I made to use a Sherline spindle as
> > well.
> > >> If you (or anyone else) is interested in this adapter, I can post
> > the
> > >> 3D
> > >> wireframe in DXF format.
> > >> You can see that I'm only using one bolt on the end plate on each
> > >> stand
> > >> off, and have no problems with vibration or flex. I think part of
> > your
> > >> problem is the standoff isn't seating well against the sheetmetal
> > >> case.
> > >> MAXNC is getting better at spin control. I seriously doubt that
> > flex
> > >> was
> > >> engineered! The whole thing is cost driven more than anything, and
> > >> it's
> > >> a decent bargin alright, but some mods will go a long way towards
> > >> making
> > >> it more useful.
> > >>
> > >> BTW, you can see in place of the stock motors, I've made thrust
> > >> plates.
> > >> There is a custom stub shaft passing through dual ball bearings.
> > >> With a nylock nut for adjustment, I can dial out backlash and
> > relieve
> > >> the motor of thrust loads. Note, this does nothing for backlash at
> > the
> > >> leadscrew nut... The Sherline spindle adapter has a constant force
> > >> spring inside that is attached to the thrust plate. I forget, but
> > >> think
> > >> it's rated for 7 lbs, and it releives the Z motor of some of it's
> > >> load.
> > >> Can also post a DXF file of the thrust plates and the stub shaft.
> > >>
> > >> As for your setup, I would suspect that either the V groove angle
> > is
> > >> not
> > >> right on one or both pulleys, or possibly one of the pulleys
> > V-grooves
> > >> isn't concentric to the bore. Does the belt vibrate or flutter a
> > lot?
> > >>
> > >> Jon
> > >>
> > >>
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