Author Topic: Square hole for cotter wedge  (Read 2814 times)

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Square hole for cotter wedge
« on: January 18, 2014, 07:54:35 PM »
I need to make a rectangular hole in the connecting rods for my Muncaster engine, for the cotter wedges, and I'm trying to figure out the best way to make this hole:



There's always filing, but only part of the hole intersects with the cut-out portion of the rod, so there's an awful lot of material to file away. Another option would be to use a broach, but keyway broaches I think are too deep to fit into the pre-broached hole. I have to start here with a drilled 3/16" hole; I'm not sure I can even widen the hole, since there isn't room for two holes that don't run into eachother.

The best I could do would be be to drill the hole against the left face (in the image) before cutting the bearing opening (so the hole doesn't wander), then cut the bearing slot, then widen the hole towards the big end. I suppose I could then file those two corners square, which leaves me with enough space for a broach 7/32" deep, which is thinner than anything I can find in duMont or Hassay Savage catalogs.

Any ideas, other than making my own broach?

Simon

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6673
  • Surrey, UK
Re: Square hole for cotter wedge
« Reply #1 on: January 18, 2014, 08:10:32 PM »
You could use a square broach to do the part nearest the rod, fit a packer and broach again to get the rectange. I'd drill out then mill with a 3/16" slotdrill and then file.

This was discussed on ME forum a couple of days ago and one suggestion to ease the amount of filing is to drill away metal from the fork end going towards the rod, that way you on/y need to file the entry and exit holes to shape.

To make your own turn some drill rod to a long taper that is 3/16 at the small end and the accross corners size at the  other then cut a series of teeth along its length. Transfer to the mill and mill 4 tapered sides, het treat and drive it through a 3/16" hole

J
« Last Edit: January 18, 2014, 08:19:31 PM by Jasonb »

Offline Dave Sohlstrom

  • Full Member
  • ****
  • Posts: 34
Re: Square hole for cotter wedge
« Reply #2 on: January 18, 2014, 08:17:47 PM »
I'm having trouble seeing how your cotter is going to hold the bearing in place with nothing to push against. Seems that your cotter should be on the open end of the slot so the bearing halves get wedged tight against the closed end of the slot.

Dave

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6673
  • Surrey, UK
Re: Square hole for cotter wedge
« Reply #3 on: January 18, 2014, 08:20:29 PM »
I expect there is a strap to go round the outside

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Re: Square hole for cotter wedge
« Reply #4 on: January 18, 2014, 09:29:13 PM »
There's a block at the end held in place with a pin (my model is wrong here; the pin just has a rounded head on one end, and I presume fits into a reamed hole through the conrod and the block, tightened down with a nut):



Jason, I thought about broaching one side, then turning the broach around. I'd be a little worried that a square broach will eat away at the sides though.

Simon

Offline Bezalel

  • Full Member
  • ****
  • Posts: 376
  • - Skype:Bezalel2000
Re: Square hole for cotter wedge
« Reply #5 on: January 18, 2014, 10:28:38 PM »
Hi Simon
 
Why not make it in two parts ?
 
mill a 3/16 slot say 3/8 deep into the top edge /(left edge as displayed) of the  wider part, then fit the narrower rod section into the top (left)1/16 of the new slot so that the square hole remaining is 5/16 x 3/16 and silver solder them together.
 
Bez
« Last Edit: January 18, 2014, 10:33:59 PM by Bezalel »
Queensland - wet one day, humid the next

Offline arnoldb

  • Administrator
  • Full Member
  • *****
  • Posts: 1338
  • Windhoek, Namibia
Re: Square hole for cotter wedge
« Reply #6 on: January 21, 2014, 05:31:45 PM »
 :thinking: Drill 1mm or 1.5mm holes in the corners, a 4mm hole through the middle followed by a 4mm slot drill (end mill will work as well) to elongate the hole, and then a 3mm mill to get closer into the corners and get the sides to size.  That should leave very little left to file out...

My 2c...

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline rhankey

  • Full Member
  • ****
  • Posts: 31
Re: Square hole for cotter wedge
« Reply #7 on: January 21, 2014, 08:28:50 PM »
If you are willing to deviate from the original slightly, you could use a shorter wedge that is a little shorter than the distance between the two fork legs.  Drill a threaded hole through the wedge, and use a threaded bolt to draw the wedge tight.  You would still use a lock nut on the opposite side.  The result would look and function the same.  With this method, you would only need to square up the through hole between the two fork legs which would be easy to do with an end mill while the rod was held vertically.  This is the method that the Stuart/Taylor Undertype utilizes.

Alternatively, if you want to remain faithful to the plans for your engine, another option would be to use an end mill to square up the through hole between the two forks (same method as I just mentioned), which would leave very little to have to hand file square at each fork leg.

Offline Zephyrin

  • Full Member
  • ****
  • Posts: 397
  • near Paris, France
Re: Square hole for cotter wedge
« Reply #8 on: January 21, 2014, 11:04:17 PM »
IMO the simplest way to do this job is by milling then filling. the difficult point is that this hole is half though metal and half in air, and drilling is not easy in this place, unless you make this hole first. In addition, the square hole seems pretty long for broaching, your pet homemade tool will be clogged with chips before reaching the way out and break ! Maybe a shaping machine-like setup like the one we use on our lathe would do it ?

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Re: Square hole for cotter wedge
« Reply #9 on: January 22, 2014, 06:58:02 AM »
Thanks for the suggestions everyone! I've already drilled a 3/16" hole on one side of the hole. I did think about using an endmill to remove material in the slot; I'd probably have to do that in the lathe since I don't have the headroom on my mill.

I'll keep thinking about it. Maybe filing would work with some kind of setup to keep the files straight.

Simon

Offline ian cable

  • Full Member
  • ****
  • Posts: 76
Re: Square hole for cotter wedge
« Reply #10 on: January 22, 2014, 10:23:58 PM »
hi mate if you clamp a small piece of gauge plate either end of the slot on your scribe lines and use a 3 cornered swiss  or stubbs medium needle file,  doing one side of  the slot at a time  your be surprised how quick it is, you will feel the file touch the gauge plate because its a lot harder hope this helps, ian c 

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Re: Square hole for cotter wedge
« Reply #11 on: February 24, 2014, 07:31:48 AM »
Thanks Ian, that's pretty much what I ended up doing. I milled away as much as I could, then made these filing guides from gauge plate, and hardened them:



Then I could fit them around the part, and hold the lot in the vise:



I'm quite pleased with the result. Certainly much easier than making a broach!

Simon