1/16" Allen wrenches rounding off corners

[Brian Rupnow]

Cams are a special case. You don't really know just what their angular rotation is going to be when they are built, and they are free to rotate on the camshaft. Sometimes, when you have assembled the engine, and turned the crankshaft/piston to exactly where it should be, if there were only one grubscrew in the cam, it would be in a position that is impossible to reach with a wrench to tighten it up. So---You put in four grubscrews at 90 degrees apart, so that at least one will always be accessible by your wrench. In a perfect world, you would remove the other three grubscrews then, and depend on the one that was left to secure the cam in position. However, the world is not perfect, and I know very well that one grubscrew is going to slip and the cam will probably move under running conditions. So, as a consequence of this turning, I leave the other three grubscrews in place and tighten them as well. All in all, with two cams per cylinder, and the fact that you never quite get the damn cam in the right place the first two times you set it, this counts for a lot of wear and tear on the end of the Allen wrench. A #6 grubscrew takes a 1/16" Allen wrench which is very small. Of course, when the edges near the end of the wrench get rounded over from use, you can always grind some off on the big belt sander to expose new crisp, unworn edges on the wrench. My 1/16" Bondhus Allen wrenches are completely worn out by the time I finish one engine. My solution is going to be either a much, much better grade of Allen wrench, or else any new designs will allow for either a #10 grubscrew or a #8 socket head capscrew--not because I need that holding power, but because they both take larger Allen wrenches that won't wear off their corners so quickly.

 

[peterl95124]

Cams are a special case. You don't really know just what their angular rotation is going to be when they are built, and they are free to rotate on the camshaft.

Brian, many of us make the cam and the camshaft from a single piece of metal, and then its the driven gear on the end of the camshaft that needs to be "timed", which you can always orient so its setscrew is accessible when the the crankshaft and camshaft are where you want them.

 

[Bentwings]

Brian, many of us make the cam and the camshaft from a single piece of metal, and then its the driven gear on the end of the camshaft that needs to be "timed", which you can always orient so its setscrew is accessible when the the crankshaft and camshaft are where you want them.

Most of guys involved with race cars are familiar with cams driven by a 3 bolt hub often with an eccentric bushing which allows the cam to be easily degrees the attaching holes are slotted you can easily model this up on cad Race engines are usually gear driven the crank is often keyed then you can use off set keys too .

 

[gbritnell]

I make my cams with a key slot. I make the gear with 2-3 keyway, one on the tooth center, one between the teeth and possibly a third splitting the tooth and space. This gives you 3 timing possibilities. A set screw would only be used to hold it in place so the torque would be taken up with the key.

 

[Rustkolector]

I use Bondhas wrenches and will stick with them. I only buy cup point black alloy set screws from Atlantic Fastener or McMaster Carr. One trick I discovered has proven out for securing cams with two tiny cup point set screws each at 90 degrees. Once you know the final placement of the cam your last step should be to install new black alloy set screws and torque the tiny ones as described here:

Set Screw Point Styles and Their Use

Jeff

 

[peterl95124]

I make my cams with a key slot. I make the gear with 2-3 keyway, one on the tooth center, one between the teeth and possibly a third splitting the tooth and space. This gives you 3 timing possibilities. A set screw would only be used to hold it in place so the torque would be taken up with the key.

George, sounds like vernier keyway slots, great idea !!!

 

[Steamchick]

Hi Shop Shoe: Your question "What is the best of both worlds?" in post #19: "My humble opinion" is a locking taper device, That has an all around torque transmission from shaft to cam, so a lot of contact area, and due o the taper-lock a high contact pressure, thus capable of transmitting far more torque than simple grubs screws. I have used a brass water-pipe olive as a simple double taper locking device where it suited my design, and other taper fitted parts are well known to work, so I won't waste space selling ideas already well known.
Where it is necessary to combine accurate alignment and torque transmission, Tapered plugs and holes are easy to make - 1 setting of the tool post can make both the internal and external taper so they match easily. And if in doubt, look at how many tapered fitted parts there are on precision machinery? - Where the Tapers are used for torque transmission. (e.g. the drill chuck in a tailstock.... etc.).
Peter T: Sorry to be "stuck in my own groove", but in this case Brian is having difficulty transmitting adequate torque from shaft to cams using grub screws (which is why he is applying too much torque for the hex. key), so he is asking for advice. We would not be discussing this if he hadn't posted his question... Perhaps I am wrong trying to fix his "tool wear" problem this way("1 Hex. key per engine" - "rounding corners"), but I think the solution is a more appropriate design for this engine than "4 grub screws tightened to death...".
I also do not like the making of precision parts, (sliding fit of cam onto shaft) only to be spoiled by - in this case grub screws - something trying to destroy the precision fit by some radial force at a point, such that the natural alignment is spoiled. Tapers retain the natural (as machined) alignment while taking-up the slack of the sliding fit of cam onto shaft (in this current design.). And a tapered plug is often relatively easy to add on the end of a shaft.... especially if like an olive from the plumber's pipe sealing tool-kit. The tapered-fitting is supplying 360 degrees of high friction (clamping force) to transmit the torque, not just the (inadequate) "4-points" as in Brian's current situation.
Whatever Brian chooses to do to make it work will be OK at the end of his job. But all advice is also read by many others, so I want to give the best advice (without blinding everyone with calculations).
But thanks for your feedback. (I am not "always right", so need feedback so others can see all the ideas).
K2

 

[Steamchick]

Thanks Rustolektor #25: I didn't know there were so many styles of grub screw - or their best applications. This is a good useful reference table.
I am sure there will be a table of "normal torques" for hex keys somewhere too.... Maybe here?
https://www.wihatools.com/pages/torque-screwdriver-blades-guideK2

 

[johwen]

Agree 100% with Steamchick. John

 

[Ghosty]

Hi All,
I don't know how it got from allen keys to a poor design of the camshaft. The number of engines Brian has built with this stile camshaft that work fine is a no brainer.
I have been looking for a decent set of allen keys, mostly 3 and 4 mm in size as they seam to wear out very quickly, as they are the main sizes that are used in RC aircraft engines.
I am just wondering if the manufactures of the allen head screws are using a slightly different size hole nowadays.
I have some 4mm L/H threaded cap head screws that are a very tight fit with the allen key, they were bought back in the early 80's, yet some new ones I bought are a loose fit with the allen key.
Shown, is just a couple of engines I am setting up for people. A DLE 130 twin, and a Satio FG90-R3

Cheers
Andrew

 

[Ghosty]

Hi All,
Just measured my allen keys, first is 1/16", then 3mm and 2.5mm, not real good for there size. At least the 3mm is almost there.

Cheers
Andrew

 

[ajoeiam]

Hi All,
Just measured my allen keys, first is 1/16", then 3mm and 2.5mm, not real good for there size. At least the 3mm is almost there.

Cheers
Andrew

If you want accuracy to 0.001" or to 0.01 mm I would suggest that you use a micrometer.
It is quite easy to get +/- 0.002" readings on a vernier caliper (been there done that!).

 

[gbritnell]

OK, sticking to the subject! I have 3 different brands of wrenches, Wiha, Bondhus and Eklind. All dimensions taken with micrometers. The size in question Imperial 1/16 or .0625 decimal. The Wiha measures .0635. The Bondhus measures. 0628-.063. The Eklind measures. 0625. Just for a comparison I measured my Eklind Metric M1.5 wrenches. The actual size should be. 05905 and it measures. 0582. I would say that they are all within a close tolerance to nominal. That leaves metal quality. That I can't judge. When I see the tip of my wrench rounding I just touch it to the grinder. I do know one thing for sure, the quality of set/grub screws varies greatly. Most S.S. screws are loose. Why I don't know. Now we're talking in the smaller sizes. Import screws vary. Good quality screws fit very well.
I use screws down to 0-80 (.035 wrench) and have no problems as long as the screw is used for an application that doesn't apply rotational loading. In my years of modeling I have found that set screws won't hold up to rotational torque applications. I don’t care if they tighten onto a flat or into a pocket. You just can't tighten the bejesus out of a set screw and not expect it to not round out. Any application involving torque needs a key of some sort and a set screw for axial retention.

 

[Vietti]

An elegant but somewhat expensive option for securing something on a shaft are Shaftloc assemblies from Stock Drive Products. I used them with satisfaction to hold the belt drive pulleys on the cam shafts of an overhead cam engine. Now using them to fabricate a starter drive on a Hoglet.

 

[petertha]

I had to look that up. Those look handy.
https://www.sdp-si.com/products/shaftloc-and-accessories/index.php

 

[ajoeiam]

I had to look that up. Those look handy.
https://www.sdp-si.com/products/shaftloc-and-accessories/index.php

Hmmmmmmmmmmmm - - - - IIRC there are a number of other similar systems.
Sorta fun how it is possible to patent an expanding driving sleeve system - - - yes?

 

[Vietti]

I agree there are other expanding sleeve systems out there. In my experience they are for larger shaft sizes and pretty large like the Browning system. I'd be interested in other model size expanding sleeve systems for sale. Can you supply references to them?

Thanks

 

[ajoeiam]

I agree there are other expanding sleeve systems out there. In my experience they are for larger shaft sizes and pretty large like the Browning system. I'd be interested in other model size expanding sleeve systems for sale. Can you supply references to them?

Thanks

Sorry - - - my knowledge base is very much skewed toward full size (grin!).
I think I would just try to machine something similar in whatever size you're needing.
Thinking I would be using a pretty good quality steel though (1045, 4140, 8620 if you can get bar end chunks - - -hopefully in sizes so you don't have to machine away piles of material).