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

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
>>
>
>
>
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe:
> CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe:
> CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner:
> CAD_CAM_EDM_DRO-owner@yahoogroups.com,
> wanliker@..., timg@...
> Moderator: pentam@...
> indigo_red@... davemucha@...
> [Moderators]
> URL to this group:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects
> goto: aol://5863:126/rec.crafts.metalworking
> or go thru Google.com to reach it if you have
> trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop
> I consider this to be a sister site to the CCED
> group, as many of the same members are there,
> for OT subjects, that are not allowed on the
> CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC
> DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN
> NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
> Yahoo! Groups Links
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
>
> CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>
>
>
>
>
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.385 / Virus Database: 268.4.5/322 -
> Release Date: 4/22/2006
>
>