View Full Version : How to make a keyway in a wheel

01-14-2005, 09:56 AM
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?


01-14-2005, 10:03 AM
Use a broach, bushing and a press.
Or you could grind a tool and slot it by hand in the lathe.

01-14-2005, 11:04 AM
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.


01-14-2005, 11:17 AM
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.). :D

01-14-2005, 11:42 AM
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/templates/product.aspx?contentid=237&productid=1319


01-15-2005, 11:11 AM
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:


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

01-15-2005, 11:45 AM
Darebee, what is your avatar? It creeps me out every time I see it!

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

ahmed drdeer
01-15-2005, 12:28 PM
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

01-15-2005, 09:22 PM
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.

01-16-2005, 06:08 AM
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.

01-17-2005, 08:32 AM
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

01-17-2005, 09:09 AM
That wasn't me poking fun Darby, I won't mention any names so as not to cause friction but, his initials were SWEDE :D

01-17-2005, 09:44 AM

Nice mail, i've come to agree with your vision that the locktite should do. The locomotive I was talking about is a 7,25" 1:8 scale live steam engine. But most of th ewheel will be mounted on the roling stock. Im going to have the wheels turned to 20,1 mm inner diameter with a chamfer on the edge not to whipe all the locktite off. Should do nicely as loktite 620 is specified to 0,35 gap size. I'd like to keep things a simple as possible as i have to make 40 wheels for the roling stock. This way the axle will be a simple piece of 20mm round steel without any work apart from cutting it at the right length.

Henk-Jan Boven

01-17-2005, 10:19 AM
Rather than machining actual clearance for the loctite, just machine a slide fit and coarse feed/ shallow thread it a little bit to give the loctite a place to sit. This will keep the wheels centered a little more easily.

01-17-2005, 11:19 AM
So, does anyone know the size of a Locktite molecule....I certainly don't but I suspect that any turned surface with a slight friction fit and Locktite is sufficient...of course we would want to use the type of Locktite that remain somewhat pliable and not the more brittle one.

01-17-2005, 05:59 PM
@ViperTX: I don't know about the molecule size, but the minimum and maximum recommended clearances should be checked in the datasheet.

@Hu: I often just machine a clearance to the minimum specified and wring it on. A motion like if you screw it on will distribute the gunk best. Then I do the last machining of the wheel perimeter with the axle between centres. No extra work, and a true running is guaranteed. It also seems that wringing it on will promote an even thickness of the Loctite, resulting in true running to begin with.

@hjboven: For the rolling stock it will be excellent. If you make a jig to get the trackwidth right, you can assemble wheels like a small factory. Do you have some pic's or drawings? I will be making some bogies for rolling too, and need some input on how to do it as simple as possible. Where do you get the wheels? I thought about getting laser cut blanks, but 23mm is too much for the neighbouring laser. And although my lathe can part off 130mm stock, my adrenaline level will go through the roof before I get all the wheels done! It's one of the most nerve wrecking operations I can think of.

01-17-2005, 07:26 PM
The bearing dia on a railroad axle is reduced from the wheel dia. That way you do not need to press it so far. If you press the wheel on use .001 to .002 press fit. The common name for the broaches is "minuteman". You need a broach bar and bushing. bob@advanced-grinding.com

01-18-2005, 08:21 AM
@ESjaavik: Making a Jig was exactley what i was planning to do. In total I'm going to make 10 double axle bogies. Might make a few more later.
I've got some drawings of bogies and wheels in Autocad and on paper as well. The original drawing has steel bearing holders that slide up and down onder load and have a pushspring to hold them down.
As I like to keep thing at a maximum efficiency level (read very simple to produce). I am alway's looking into alternative way's. So the axle is now 20mm over the entire length and not machined to 17mm at the bearing. Making an axle has been reduced to ordering some 20mm round bar steel :-) Maybe polish it a bit and the wheel machined to 20.1 mm will slide fit to its position with locktite 620 to hold it in place.
The original Bearing holder was designed to acomodate a SKF ball bearing. But I would have to machine 40 bearing holders with my mill and spend some Euro 180,- on the bearings themselves. I thought I'd keep it simpler and have ordered some hightec plastic called "Murpec SP" to machine in the shape of the bearing holder but actually with a 20mm hole. To use it as a slidebearing as it is well suited for this. Have a look at http://www.murtfeldt.de/de/werkstoffe/direktwahl/murpec_murpec-sp/ I need a piece of 20*40*2000 wich is only 115,- here locally that's already less than the bearings themselves I would need otherwise. And I will never have to lube the roling stock :-) The wheels themselves I am ordering them at a local machineshop. With my cad drawing of the wheel profile the can produce them with their CNC lathe/milling machine. You know such a highteck 5 or 6 axle machine that seem to do everything automa(t/g)ical. Cost wil be less than 15,- for a wheel in simple steel 37 quality.
Ive designed the wheels to 7,25 inch narrow gauge standards since these are a little wider and have higher sides that are more forgiving to your track an will derail less than normal gauge type. Have a look at http://www.jeugdland.net/index.php?page=35&section=1 and you will see our track. We have about 600 meters of tracklength.


01-18-2005, 01:13 PM
Aw Darebee, now you've gone and changed your avatar. I miss that galloping purple monster. Whatever it was!

01-19-2005, 09:35 AM
It was green but thanks for noticing.
Homer is kinda boring though.

01-19-2005, 09:51 AM
I agree with Swede DareBee, I kinda miss him, when ever I saw him I felt compelled to sit up real straight, put my two fist straight ahead about shoulder height as if I were grasping a set of reins and then imagine my self galloping away :D

01-21-2005, 10:59 AM
Your vivid description causes my head to flash very realistic (and disturbing) images involving sheep and rubber boots.

01-21-2005, 01:34 PM
I'm pretty sure that the "monster" was a llama, although it must have been the chlorophylled kind ;)

01-26-2005, 08:42 AM
If you have a lathe, you may be able to rotary broach a shape into the wheel also. This is probably an expensive option for just a few wheels, but you could pick rotary broaches in any shape; keyway, spline, etc. - www.rotarybroaching.com

01-27-2005, 10:38 PM
$150.00 will do, and I get you a magic answer (chair)