View Full Version : Making a rack and pinion...

09-11-2005, 06:43 PM
I need to make a little rack and pinion for this old TIG pedal. Here is what I need to do:
The pedal throw is 1.5 inches and the pot I need to actuate turns 270 degrees. I'm planning on making the parts out of al.

I guess I need to figure the throw of the pedal and figure out the circumference of gear needed.

I'm limited in the gear cutting dept/ number of teeth to this:

Any advice?

I just wanted to add that I'm just wanting to cut a spur gear. No involute or fancy stuff involved.

Deep Sea Tool Salvage

[This message has been edited by hoffman (edited 09-11-2005).]

09-11-2005, 07:45 PM
Gosh, I'm sorry to see how limited your resources are. http://bbs.homeshopmachinist.net//biggrin.gif

Here's what I cobbled up to control speed on a tool. I haven't even made the cover yet. Once you have the throw necessary to get full pot rotation, you can make the pedal arm fit. The rack and gear came from my stash of "might use it some day".

Another option is to look for a "Wah-Wah" pedal commonly used by guitarists and other musicians.


09-11-2005, 07:58 PM
Thanks Ken! That's pretty much what I had in mind. What I meant by limited is the fact that that little indexer is limited to the # of holes in the plate. I'm not sure how well it'll do with cutting a spur but the shaper should have no trouble cutting a little rack.

There may be some clearance issues using the indexer on the shaper.

I used the crap out of it making parts to fix it up but haven't touched it since it was finished http://bbs.homeshopmachinist.net//rolleyes.gif

I didn't think about a wah pedal. Maybe I could just change out the pot and add a microswitch for the arc start... thinking...

Deep Sea Tool Salvage

[This message has been edited by hoffman (edited 09-11-2005).]

J. R. Williams
09-11-2005, 08:16 PM
Consider using a section of an old steel tape measure blade and wrap it around a drum on the shaft of the control pot. I built my unit from a rack and pinion that came with a hand actuated control but would have gone the tape route otherwise. Check the Home Metal Shop Club web site and look for "Foot Actuated Welder Control" in the article index. There are two photos of my unit.


09-11-2005, 08:44 PM
Thanks JR! I just spen some time looking through the articles. Great resource!
You guys have given me some great Ideas.

George Barnes
09-11-2005, 09:53 PM
Is this anything like what you are looking for.


I took the cover off of my Linde TIG foot pedal unit and shot this pic. According to my elcheapo gear pitch gage, it is a 32 D.P. and the pinion is an 18 tooth. On mine the travel is about 1-7/16". The pitch diameter should be .562" which would give a circumference of 1.766" and that comes out to about 292 degrees for the 1-7/16" of travel.

Hope this helps.

09-11-2005, 09:59 PM
One other way of doing this ( attaching a pedal to a pot) is to use a knee linkage between the pedal and a collar on the shaft of the pot with a small arm soldered onto it. You can only get about 180* of turn this way so you just use a pot about twice as large as you need and then only use half of it. This is how I made some foot pedal light dimmers. Works great.

Another way to do this is to wrap a string about three turns or so around a pulley on the shaft with the ends attached to the heel and toe of the pedal thru two pulleys and kept tight by a spring on one end.

09-11-2005, 10:01 PM
<font face="Verdana, Arial" size="2">Originally posted by hoffman:
The pedal throw is 1.5 inches and the pot I need to actuate turns 270 degrees.

I guess I need to figure the throw of the pedal and figure out the circumference of gear needed.

For 1.5" throw the pot gear should be around .480" in diameter. The .48" will give a circumference of 1.5" or so and with the 270 deg. you will have a little room the fine turn or adjust. JRouche

09-11-2005, 10:11 PM
Hi There,

Depending on how cheap you are (or challenging you want), you can get brass racks and pinions from Mcmaster-Carr.

Good Luck!
-Blue Chips-

09-11-2005, 10:26 PM
If its the pinion you need, go to a hobby store and buy an R/C car pinion, I think 32 pitch is a standard one. I just did that to fix my slide projector focus, needed a 48 pitch 19 tooth.

09-11-2005, 10:42 PM
Lots of creative solutions for this one!
Here's the pedal I have:
The resistor that's in it is a slider with the wiper on the arm. There is plenty of room in it for mounting a pot/linkage.

The micro switch on the left is the arc start and the steel rule is to give some scale.

Thanks for all the input!

[This message has been edited by hoffman (edited 09-11-2005).]

09-11-2005, 11:37 PM

Are you related to me?


09-11-2005, 11:57 PM
There's always ebay...

http://cgi.ebay.com/Gear-Rack-11-South-Bend-Lathe-model-27A_W0QQitemZ3872937051QQcategoryZ25290QQssPageNam eZWD1VQQrdZ1QQcmdZViewItem

Have fun,

09-12-2005, 10:19 AM
I don't know Dave. We're both from Ga., we both drag home some crazy stuff and we both seem to use the same systems to organize our shops...
What do you think about this welder deal? It goes from 2 amps to 300 and has hi freq. Hope I'm not wasting time and $$...

09-13-2005, 01:11 PM
What about just using a slider pot of the same value? A linkage has gotta be a lot easier than R&P. I've made FX pedals like this.
Rgds, Lin

09-13-2005, 01:48 PM
I don't know what resistance range is required but I would be tempted to go with a much simpler system. Use a cadmium sulphide photocell with a night light bulb shining on it. Between them and attached to the pedal is a vane with a vee shaped slit. As the pedal is pressed the amount of light falling on the photocell varies which varies the resistance. Only one moving part. If the bulb burns out it goes to max resistance which is a fail safe.

09-13-2005, 02:00 PM
Wow Evan that's pretty clever! It requires a 1000 ohm 12.5 watt pot. The one that comes on it is a big honkin' ceramic wound deal that looks like it belongs on a battleship. The problem I've had is finding something that's rated at a high enough wattage.

Sparks, I couldn't find a 12.5 watt slider. About the largest I could easily find was 5 watts.

I have one on the way via mail order but I found another one today. I guess I'll have 2 now...

09-13-2005, 05:20 PM
<font face="Verdana, Arial" size="2">Originally posted by hoffman:
The problem I've had is finding something that's rated at a high enough wattage.

Sparks, I couldn't find a 12.5 watt slider. About the largest I could easily find was 5 watts.

I use a very common headlight dimmer switch from an early chevy for one of my "projects". They have a wattage rating between 240-360 watts. JRouche


09-13-2005, 05:41 PM
Oh well. I don't think they make 12 watt CDS cells. I have some 50 watt wire wound ceramic tubular resistors with sliding tap. It would be easy to make a slider for one actuated by a simple lever linkage. I don't know if I have any at 1000 ohms. If I do you can have it for shipping. I'll look tonight.

09-13-2005, 05:46 PM
Evan, If you look at the picture you can see that the pedal already has a wiper. The resistor you're talking about would be the perfect solution.
The pot I rounded up is burned out http://bbs.homeshopmachinist.net//frown.gif

09-13-2005, 09:34 PM
Look for Rheostats instead of Potientometers for high watt applications. I wonder if you could use this 750ohm? For $1.89, it might be worth a try. Most wire wounds are 15-25% anyway.


Here's the catalog link:
http://www.surpluscenter.com/item.asp?UID=2005091321070922&item=11-1927-C&catname=el ectric (http://www.surpluscenter.com/item.asp?UID=2005091321070922&item=11-1927-C&catname=electric)

[This message has been edited by CCWKen (edited 09-13-2005).]

09-13-2005, 10:05 PM
Sorry to get your hopes up Hoffman, the largest value I have is 100, not 1000. I couldn't remember as I haven't looked at them for a while.

09-13-2005, 11:50 PM
OK, so a low power slider pot and a TO3 or TO220 power transistor? (or 2, or 3....)

09-14-2005, 01:49 AM
12.5 watts isn't a lot of power for a transistor. A single TO-3 would be enough, or one of the plastic packages made for clamping to a heatsink. The transistor could be controlled by the cds cell.

Of course, you'd have to understand the circuit to know whether the mod would work. Chances are there's ac there and a semicomductor wouldn't work in that circuit.

[This message has been edited by darryl (edited 09-14-2005).]

09-14-2005, 05:05 AM
Yup, yer right Daryl. Sorry, this isn't the place to go into triac operation http://bbs.homeshopmachinist.net//smile.gif