Re: Need help to decide what rack and pinion to use in a 6'x10' table

Hi Jarrett,
In some posts from cnczone ive seen some mods of pre-laods, I think
a plain good selected spring will do the trick, I seem different
ways of acomplishing this, some also recomended by 'Al the Man' I
tend to go for the 20 PA but it seems I can get it anywhere online.
14.5PA is available from lots of source, ex. mcmaster but 20PA not,
if you know where i can get it from, please send the link...
Regards,
Hector
--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jarrett & Heidi Johnson
<hjjohnson@...> wrote:

>
> Hector, just a side note. If your running rack and
> pinion. I'd recommend using some type of pre-load,
> to push the pinion into positive contact w/ the
> gear. I'm using rack and pinion [ well not using
> yet as its still getting built] but I'm going to
> use two gas shock's per each pinion/drive
> assembly. This will cover for any variation on the
> rack mounting, by allowing the pinon to 'float' in
> contact w/ the rack. There are forces that are
> trying to push the gear back out of the rack when
> its being used and they can be calculated and then
> you base your pre-load force on this number. I
> still think you should go w/ 20PA. It's been
> recommended to my by others who have 'been there
> done that'. Do some Rack/pinion searching on
> cnczone.com and watch for 'Al the Man' as he's one
> of those guy's who know's what he's talking about
> .. [and no.. thats not me :-). Mind you.. I did
> reply to your post on there..]
>
> Jarrett Johnson
>
> ----- Original Message -----
> From: "Hector" <hector_a_quintanilla@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Sunday, April 23, 2006 5:34 PM
> Subject: [CAD_CAM_EDM_DRO] Re: Need help to decide
> what rack and pinion to use in a 6'x10' table
>
>
> > Hi, folks, thanks for the replyes,
> > Ballendo,
> > I see you mention you are using steppers, in my
> > case i want to use
> > servos.I dont realize if you have to take
> > different aspects into
> > account in the decision of what rack and pinion
> > if your are using
> > seros or steppers. To make it clear does it
> > matter what kind of
> > motors are you using in the rack & pinion
> > decision?
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com,
> > "ballendo" <ballendo@>
> > wrote:
> >>
> >> Hello,
> >>
> >> Snips, inserts below...
> >>
> >> >In CCED, "Hector" <hector_a_quintanilla@>
> >> >wrote:
> >> >Hello,
> >> >Im confused on which combination of rack and
> >> >pinion to use for a
> >> >6'x10' table.
> >> >1.- which presure angle (PA) to choose, 14.5
> >> >PA or 20 PA?
> >>
> >> I have long used and suggested--look in this
> >> group archive for my
> >> many previous posts-- 14.5 Pressure angle, as
> >> it will minimise
> >> backlash caused by changes in pinion to rack
> >> distance.
> >>
> >> Others have replied that the undercutting of
> >> teeth on small
> > pinions
> >> using this PA is not a good thing, and mention
> >> that certain
> > machines-
> >> -including Bystronic CNC laser cutters--use
> >> 20PA.
> >>
> >> I still prefer and suggest 14.5 PA. (But would
> >> use 20PA for
> >> a "lightly loaded" machine, where I might want
> >> to economise by
> > going
> >> with a smaller rack and DP.)
> >>
> >> >2.- after knowing what pressure angle will be
> >> >used, the next step
> >> >is to decide the diametral pitch to use.
> >>
> >> The DP (Diametral Pitch, which is the number of
> >> teeth in a one
> > inch
> >> gear) affects cogging, strength, and cost. I
> >> use 16DP. Coarser
> > gears
> >> can carry more load, but also are more
> >> susceptible to backlash
> >> (especially is 20PA is used.) Smaller
> >> teeth--larger DP--will have
> >> less ability to endure shop swarf and dust, and
> >> a lower strength.
> >> They may even cost more. 16DP seems to be a
> >> good compromise for a
> >> 4'x8' or thereabouts size machine...
> >>
> >> >3.- In this step we already know the PA and DP
> >> >we are going to
> > use,
> >> >now comes to decide how many teeth on the
> >> >pinion, so what governs
> >> >this decision?
> >>
> >> I nearly always use a 1" pinion. This gives
> >> about 3" of travel per
> >> rev, and is large enough to have reasonable
> >> undercutting of the
> >> teeth in my preferred 16DP.
> >>
> >> What governs this decision is your speed and
> >> resolution
> >> requirements. Larger pinion equals faster
> >> speed, but a lower
> >> resolution, all else being equal.
> >>
> >> I use a 4:1 reduction from motor to pinion, so
> >> in the old days<G>
> > of
> >> halfstepping, I would get 240IPM at only 300
> >> RPM at the stepper.
> >> This kept the drive cheap, and was plenty fast.
> >> The resolution was
> >> traded to get speed, as it was only about
> >> .002". (500SPI)
> >>
> >> Using modern drives and motors, you can easily
> >> exceed these
> > results.
> >>
> >> >I think is better if someone could really make
> >> >clear this for me
> >> >and others, i guess other have the same
> >> >doubts.
> >>
> >> Hope I've donethat!<G>
> >>
> >> Ballendo
> >>
> >
> >
> >
> >
> >
> >
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