2

I have a very old (1940's) Kenmore stove/oven that has almost no info online about it -- and have been looking and failing to find replacement knobs for years now. It has an extra large D-shaped gas connection that fits inside the knob, and no universal or "Kenmore/Roper" knobs are big enough.

How might I handle this -- is there a mortise bit for this sort of thing?

If not, I guess I drill a hole, cut the wood in half along the center of the whole and glue a flat part to it? That is where I am headed...

EDIT: This is the model

Here's a pic Kenmore/Roper Knob

10
  • Have you tried the big bay auction site for parts for your vintage range model? Drill round hole, use a small chisel to flatten the curve on one side. ?
    – Alaska Man
    Apr 21 at 19:01
  • 1
  • 1
    Hi, welcome to Woodworking. We could do with a photo of the spigot (?) to get a better idea of the exact shape you need to allow for (it sounds from what you've said that it's actually a semicircle, not what I imagine when I think D-shaped). A sort of 'standard' D can be a simple drill-and-chisel job but perhaps the easiest way to make a semicircular mortise is just to drill a hole, then simply plug one half of it. This doesn't even need to be plugged with wood (i.e. a dowel sanded or planed down to half width) in theory you could do it with filled epoxy or an epoxy compound, for an exact fit.
    – Graphus
    Apr 21 at 20:54
  • It's of course totally outside our scope, but had you thought of 3D printing as a route to a replacement knob? I believe stove restorers (yes, that's a thing) commonly use this method now, although I think it's not unusual to make a mould from that to cast the replacements in a harder and more authentic looking resin, but sometimes the 3D print itself is used so the print material can be well up to the task.
    – Graphus
    Apr 21 at 21:25
  • Pics or it didn't happen.
    – jdv
    Apr 21 at 22:06
7

It appears from the description and the photo that the stub cross section is in essence a circle with a chord removed, basically it's a cylinder with a flat bottom. The easiest way to create a matching mortise in wood is to drill a hole of the major diameter, then partially plug it.

For a wood-only solution a small piece of dowel sanded or planed down is probably the easiest option for adding the flat. Although a face-grain plug would arguably be stronger I'm not sure it would matter, and anyway plug cutters are available in a much more limited range of sizes than dowel1.

If, as clarified in the Comments, the knobs are all going to be replaced then their shape can be much simpler, so the strength of the starting material matters less than it would if the complex form of the original knobs were being recreated. So any good, dense hardwood should suffice. Oak wouldn't be my first choice but I bet they'd outlast you. Maple would be a superior option (noticeably harder and not open-grained) but its pale colour is likely to become an issue in terms of them getting grubby with extended use. If I used maple I would consider painting them with something really tough, or alternatively staining them very dark so that if/when a clear finish wears off grubby marks are far less visible.

Consider adding a grub screw
A screw driven in through the 'bottom' of the handle at back would ensure they won't work loose over time, while still being fairly easily removable. But more than that, you could use this to avoid having to create the flat side of the mortise entirely — the screw can do all the gripping if required.

The screw length should be carefully tailored so that it pinches the stub, but does not project from the wood. Any machine screw or bolt of suitable diameter can be suitably modified with a hacksaw or junior hacksaw (to cut to length and to saw in a screw slot) and a grinder or file (to round the tip).

The hole to accept the grub screw does not need to be threaded in advance. But if you wanted to do so and don't own a tap-and-die set you can easily create an ad-hoc one, see bottom of this Answer.

Regardless of whether you thread in advance or not the walls of the holes can be strengthened by dribbling in some superglue/CA. This isn't strictly necessary 2 but by all means do it anyway if you want, it can't hurt.


1 If necessary the dowel could be custom made in the shop, the simplest method being to make a suitable dowel plate, see second half of this Answer.

2 Forced-in and cut threads in strong hardwoods are very durable, even when regularly used which they won't be here.

4
  • Ooooh... Nice lateral thinking!
    – FreeMan
    Apr 22 at 17:19
  • I hadn't really considered machine screws into hardwood before, but that sounds useful. Would you say there's a minimum size for the threads to be secure? Here it looks like M6 or 1/4" would be an option and I'm sure they'd be coarse enough, but much smaller and I'd have my doubts, and the pilot hole would need to be more precisely sized
    – Chris H
    Apr 30 at 7:31
  • Of course grubscrew-fastened knobs are very common, and it might even be possible to buy something suitable
    – Chris H
    Apr 30 at 7:31
  • I guess M6 or 1/4 20 UNC would be a good no-worries size; while I'm fairly sure M4 would work fine if you have the space then no real reason not to use either larger size.
    – Graphus
    Apr 30 at 11:11
4

You could drill a hole the the exact size of the semicircle and then on the one side you could chisel out a square section large enough so you could insert a small block of wood (1/4"1/4"x1/2"long) which fills the chiseled section as well as into the drilled hole to complete the semicircle.

Not sure if this is the easiest way but it is an option that has not been suggested so far.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.