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/diy/ - Do It Yourself

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rack & pinion help

Hi all. In need of some help. To preface - I'm very, very stupid and I basically need babied for this. If that is not something you want to do, I suggest passing this thread by.

I have a rack and pinion that seems to be very non-standard.

Round rack.

~12mm OD.

Pinion gear

0.8750" OD

30 teeth

~.08" pitch

69mm travel on rack for full revolution of gear.

Pressure angle presumably 20*

Cannot find this for the life of me, and there also doesn't seem to be a lot of literature about rack and pinions online?

I can resign around this within a decent range.

Rack length is 269mm. Sorry for mixing metric and imperial btw.

Can use .5" OD rack because I presume it's more easily sourced. What other info am I missing to find the proper rack?

Thanks in advance. Any input is much appreciated
>I have a rack and pinion that seems to be very non-standard.
Where, what is it in, and can you post a pic of what you actually have instead of stock imagery

>Cannot find this for the life of me, and there also doesn't seem to be a lot of literature about rack and pinions online?
Have you tried Machinery's Handbook?
First off, gear racks are mostly bought from suppliers such as this one.


Even the selection of gears and gear racks from large suppliers like McMaster-Carr will be pretty limited. Find the gear rack in the size, pressure angle, and length relevant to what you want to do. Then source a gear with the same pressure angle and pitch diameter that you want for the load and travel rate required.
>Round rack.
Do you mean a round driveshaft with a gear rack cut into it? Those aren't that common in the first place. And you're asking for a metric OD on one and then imperial measurements on the pinion gear.

>~.08" pitch
That's not a valid pitch number. See diagram
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stop panicking. the part is standard.
It's close to their mod0.8, but when using their provided measurements, it's off by about .5mm

Still think that might be it?
no. what the fuck part of "5 teeth in a cm" "2mm between teeth" looks like mod0.8!? you imbecile, did you hold it up against the picture ON YOUR FUCKING SCREEN
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please dont talk to me that way.
Bruh this is op. Why are you on diy if you're so angry.

I printed it out and compared. The CLOSEST thing on this list is mod0.8

Tell me what I'm doing wrong?
Does the scale in the lower right-hand corner match a ruler?

Nearly. Close to 95% I think, lines were a bit thick. I checked ratios tho. It's about 10% off mod0.8 if my calipers are correct. I'm planning on just calling them in the morning

The part is close to mod 0.8 and nothing else, but it doesn't match up to mod 0.8

Confused on why you're telling me it's standard. Am I missing something?
pls help
Do you need a replacement rack? What's this even for, what product did this assembly come out of?
I would assume you want a replacement but your original post is and you said you "need babied" for this one so I don't know.

It's just a pre-existing custom assembly that has no documentation. I'm tasked with creating documentation/a BOM for it so that it can be re-created.

I do in fact want a replacement rack and I'm trying to get exactly what we have, but it seems ever so slightly non-standard (was probably made in Britain from sketchy parts suppliers)
I'd bring the rack and pinion into a machine shop and ask if they could help with identifying the tooth pitch.
Looks like a custom machined part to me since it's roundish and has a few flats machined into it. This means just buying any rack from a hardware supplier won't be what you need, it's gotta be machined.
Does the tooth pitch have to be exact? If you're replacing parts why not also replace the spur gear?

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