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

Hector, Make sure you use a strong spring. There
is more force there than you'd think. For my
system. I'm using a 640 oz-in stepper, it goes
through a 10:1 gearhead and the out through a 2"
pinion gear to my rack. This gear will put about
400 lb's of force to move my gantry. It will also
put about 146lb's force, trying to push the gear
out of the rack, so that's enough to need a fairly
strong spring.. or a pretty long arm on your
spring.. or both.

Can I ask you where your located [city/state/town]
I'll find you a couple suppliers for rack/pinion
stuff nearby. [feel free to send it to me directly
instead of on here if you wish.]

Jarrett

----- Original Message -----
From: "Hector" <hector_a_quintanilla@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, April 25, 2006 5:12 PM
Subject: [CAD_CAM_EDM_DRO] 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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> CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC
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> List Mom
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