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Searching for an Off-The-Shelf, Light-Duty, Rack & Pinion

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Martin McCann30/07/2019 21:22:49
3 forum posts

Hi All,

I'm asking for suggestions, please, for an off-the-shelf, light-duty, rack & pinion.

It's for my Misses to raise & lower the roof of her camper-van, which isn't motorised.

The distance of travel is just under a metre, so a 1m rack would be perfect.

The maximum load would be 25kg, so I reckon a rack based on 6-8mm square bar would be more than adequate in steel(?), or 15-20mm square in nylon or hard plastic.

The tricky part could be the pinion. I'd like it to be held, fixed, onto the rack (except when screwed right off the end).

I plan for her to to drive it up & down with her battery-powered electric drill, with the right bit coupled to the pinion.

I'm not a mech-eng, so I haven't done any maths on this but my gut feel is that it's a viable plan. Any comments appreciated, especially where I might get the rack & pinion. I have access to a workshop, so I can adapt & improvise to a degree.

Many thanks, Martin.

vintage engineer31/07/2019 08:36:46
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252 forum posts
1 photos

**LINK**

Chris Evans 631/07/2019 09:17:19
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1667 forum posts

HPC are my go to, also look at Duval Gears. I think your 6/8mm square bar is a dream that will be flexible there will be no strength or any depth for the tooth form. Start thinking around 15x20mm.

magpie31/07/2019 09:23:39
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457 forum posts
80 photos

A timing belt, a strip of metal, and some super glue.

Juddy31/07/2019 09:33:00
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67 forum posts

Hi Martin have a look at rack and pinion jacks such as these: **LINK**

or something like a green house window opener like these: **LINK**

Samsaranda31/07/2019 09:37:15
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934 forum posts
5 photos

I always use HPC for anything to do with gears, good products and excellent service.

Dave W

Ian S C31/07/2019 13:11:56
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7468 forum posts
230 photos

Find someone who sells parts for floor standing drill presses, The rack on them(talking of Rexon), is rubbish. A number of years ago I was working with a mate over hauling Willys Jeeps, and Doug the owner put the cylinder head of the Go Devil engine on the table of the drill press, a bit low, unlock the table height,BANG, oops. A new one was only about $NZ3, don't know about the pinion.

Ian S C

Clive Foster31/07/2019 14:19:49
2206 forum posts
73 photos

An alternative way of doing the job might be to re-work one of the inexpensive 12 V electric linear actuators that can be found on E-Bay et al for £25 - £30 if 2 to 4 inches of travel will do. Basic idea is to replace the existing telescopic tube guide system with an external rail with a nut block running up and down it. Screw needs to be far longer. Either replace with standard threaded rod or trapezoidal thread lead screws aren't silly expensive. Maybe £10 - £15 per metre and as much again for nuts.

Looked into similar some years ago for a friend and planned to use a 3/4 square tube as the guide for a nylon sliding block with the original nut converted into an insert to take a longer version of the old screw. Plan A was to re-machine the end of the screw to sit into the standard gearbox. Plan B was to simply chop the original screw and couple it to the new one via UJ or similar coupling.

Darned if I know why the job was never done. Got some drawings based on re-working a Hiwin brand actuator on the computer. Used a 3 mm pitch by 11 mm Ø screw according to my drawings.

Clive

Martin McCann31/07/2019 20:17:15
3 forum posts

Thank you all for these excellent suggestions. I couldn't have come to a better place for advice.

Tim Chambers31/07/2019 21:10:35
82 forum posts
33 photos

Something like this perhaps?

linear actuator

Jon Lawes31/07/2019 21:25:54
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371 forum posts

The other day I saw a scrap built go-kart that used an interesting bodge as a rack and pinion; a straight piece of square rod for the rack with a short length of chain tack welded to the top. It certainly made me think.

John Duncker 101/08/2019 20:00:01
32 forum posts

I meter of threaded rod. 1 nut welded to a bracket some swivelling allowance. I electric screwdriver. All cheap as chips.

Just hold the driver to stop it turning?

You will have side load issues with a rack.

Dave Halford01/08/2019 20:54:52
759 forum posts
6 photos

Is this roof hinged on one side if so 2 gas struts would do it.

Ian S C02/08/2019 10:24:57
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7468 forum posts
230 photos

Perhaps a bike chain and sprocket, could even be motorized with a wiper motor, extend the worm wheel shaft so that you can fit a sprocket.

On a similar line to Jon Lawes, I have tacked a chain around a steel disc to mesh with a sprocket. A rough and ready rack could be made with a bit of square tube with a row of suitable spaced holes, and a small sprocket from a bike, the holes could be drilled about 5 mm and squared.

Ian S C

Martin McCann02/08/2019 17:08:16
3 forum posts

More great suggestions. Many thanks to all of you.

Hollowpoint02/08/2019 18:40:36
331 forum posts
31 photos

There's a few racks on ebay from old lathes about the size you are after. Might be worth a look. 👍

Clive Foster02/08/2019 19:10:53
2206 forum posts
73 photos

A chain rack isn't a bodge. Correctly engineered and properly supported it's an excellent method of accurately transmitting motion. Frequently advocated where part circle movements are made as running a short length of chain around a part circle is probably easier than cutting gear teeth.

Adcock Shipley used this type of construction to drive adns et the head tilt on versions of thier smaller vertical milles fitted out to make tooling for grinding lenses. A job that needs tob e accurate and easily done if you don't want to spend ages getting it dialed in. The one we had was certainly accurate and quite easy to use.

Chain type rack is very low friction so, in vertical application, its necessary to control any tendency to run back.

Clive

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