How to make a keyway in a wheel

[hjboven]

Dear all,

I'm working on a model locomotive an encoutered a problem fixing the wheels that I'm not able to solve yet.

I need to fix some wheels onto a 20mm axle. I dont want to trust solely on loctite as they wil be driving wheels and subject to some torque. Heat shrinking is a no go as the weel needs to go at least 15mm down the axle to get to their mounting point. (bearings are on the outside)
So I thought of fixing them using a keyway. but how do I make a keyway inside the wheel in a 20mm hole?

Regards,
Henk-Jan

[DareBee]

Use a broach, bushing and a press.
Or you could grind a tool and slot it by hand in the lathe.

[edbo68]

You can get broachs from any machinist supply.
Travers in thier catalog has a picture of the process for broaching on page 268.
This will give you an idea how it's done with a broach.

https://travers.com/pdfshow.asp?p=268

[Al_The_Man]

Of course you could conform to true scale detail and mount them as railroads in N.Amer, do anyway, that is to bore the wheel for a friction fit and press them on to a certain tonnage ( in the case of actual loco.).
Al

[hjboven]

Thanks edbo68, looking at your link I now know what to look for.
Found it in a dutch shop now to. A nice shop by the way. http://www.buitelaar.nl/comasy/templ...productid=1319

bye,
Henk-Jan

[Swede]

One can do super-tiny keyway slots as Darebee mentions. quite cheap, on a lathe. Keyway broaches only get so small. I needed to cut a really small keyway in a bevel gear, and ground a shaper bit to do so. See the first two pictures here:

http://www.5bears.com/dist.htm

Darebee, what is your avatar? It creeps me out every time I see it!

[Ken_Shea]

Darebee, what is your avatar? It creeps me out every time I see it!
LOL

You can also plunge cut with a end mill of correct size and file the radius to square.

[ahmed drdeer]

hello
you may drill the wheel and the shaft together until you reach about 5 mm depth in the shaft then you can tap the wheel alon and tiyed them together whith a screw this
is a defrent idea instead of key way and it's up to you
best wishes

[Konrad]

Or you can just drill, like ahmed has mentioned, then install a pin, instead a square key.

I have done it on slitter blade holders, works well.
Konrad

[ESjaavik]

You don't tell what kind of a locomotive this is. If it's a steam locomotive, the keyway may be the scale correct solution. If that's not an issue, locktite should be fine. Use it even if you use a keyway. If the keyway/key is not 100% tight fit, there may be problems with the key and slot "forging" each other.

Let's play some numbers:

Your 20mm axle have 62,8mm circumference. If it also is 20mm depth, you have 1256mm^2 surface. With Loctite 638 that joint would hold >31400N. It's on a 0,01m radius, so the torque would be 314Nm. That means if your wheel is 200mm diameter, each wheel can pull 3140N before it breaks the bond. Generally you can assume a friction coefficient of 0,2 between wheel and rail. So to get that static torque, you would have to load each wheel with 15700N, or about 1,5 metric tons!

How much do you have to degrade to take up shock loads? I don't know, but I would feel happy with 10:1 thus 150Kg/Wheel should be fine.

I cut my wheel bosses first to a tight sliding fit. Then I cut it somewhat oversize except from the outer 1mm. This is to assure a concentric fit, while still allowing space for the Locktite. Also there should be a well rounded edge on the inside so it does not scrape off the Locktite. But you will need that anyway to clear the rounded root where the axle diameter increases.

Make an axle stub welded to a steel block and a boss from the same materials you plan to use. Machine to the same tolerances and fix them together. Attach a long bar to the boss, and fix the steel block in a large vice. Try to break the bond. I think you will be surprized. If you need to break it, heat the joint first. Then the bond will be weakened and you can pull the wheel off by it's boss, NOT the rim!

If you want to press fit, make the boss and axle 0,1mm larger than your bearing ID. Then the wheel will pass over the bearing seating without marring it. You will of course need a "push tube" a bit longer than the remaining axle stub after the wheel is pressed on.

BTW: Do you read German? Then for steam model related advice, try this: http://27933.rapidforum.com/ As I'm writing this, it's down because of a technical problem, but try later.

[DareBee]

I usuall use the method Swede depicts only for blind keys but it definately works.
I also toyed about mentioning the drilling method that Ahmed posted but I noticed you said the wheel is15mm in from the end of the shaft (which changed my mind).

Ken - I thought that avater was super funny.
I will change it - just for you buddy

[Ken_Shea]

That wasn't me poking fun Darby, I won't mention any names so as not to cause friction but, his initials were SWEDE