1/16" Allen wrenches rounding off corners

[Brian Rupnow]

I use a lot of #8 grubscrews on my engines, especially to hold the cams in place on the camshaft. I simply can't keep my 1/16" Allen (hex end) wrenches form rounding off when I tighten these grubscrews. I use "Bondhus" made in USA wrenches. Are there better quality Allen wrenches available, and if so who makes them. This issue is driving me crazy.---Brian

 

[ChazzC]

I haven’t had issues with my Bondhus allen wrenches (ball end keys & screwdriver style, all “Protanium”), not even the 0.050” one. The good news is they have a lifetime warranty, and I don’t think you need to return the bad one(s).

 

[Vietti]

You can, of course. simply grind of the rounded portion an you are good to go. Might consider going to a larger dia. set screw to get a more robust screw socket.

 

[Emers]

Hi Brian
I am a 73 year old machinist and I have the same problem, I have noticed the the problem is not always the allen wrench itself but the hex in the grub screw being to large. I try to buy better quality allen wrenches and better brand grubscrews here In Australia I try to purchase Unbrako as they are generally a tighter tolerance fit. There seems to be a lot of rubbish form Asia out there

 

[petertha]

I'm turning into a Wera fan boy even though they are pricey. The metallurgy is good but they must also tweak the shape as well, they just fit & bite better. I found the same for Torx. As mentioned the bigger challenge is low quality screws these which influence fit. But I have yet to see anything approaching wear on the tool. I do a lot of metric small fastener stuff & have reground Bondhus quite often compared to even offshore hobby drivers so I don't think Bondhus is anything special. And when it comes to ball ended requirement, regrinding isn't an option either.

https://www.kmstools.com/wera-hex-plus-9pc-hex-key-set-metric.html
https://www-de.wera.de/en/great-tools/hex-plus/

 

[Mike Ginn]

My experience is identical to Emers. eBay is a very convenient supplier of all things including almost any size of screw/socket head. I have found that the sockets are usually oversize especially the smaller grub screws. You just can't torque them up. I now buy from a screw supplier and pay x10 more but guess what - they can be torqued and the Allen keys fit.

 

[johwen]

Hi Brian, get "UNBRAKO" brand keys and screws. I had the same problem until I upgraded my grub screws and Keys. John

 

[Steamchick]

Hi Brian, I can't add any more to the advice above, but good screws and keys cost more and come from reliable suppliers. Cheap comes cheap from anywhere and often fails in service.
BUT, being a mechanical "nerd" I suggest that a simple locking screw is really innadequate for cams operating valve gear. The torque magnitude and tortional oscillations will work the screws and cause them to slacken, if the contact point is not the centre of the grub-screw. If the grub screw is a sharp point into a machined matching hole, it may be OK, BUT a design that uses precision tapers, keys, or something that can handle the torque oscillations is really necessary.
Personally, for small work, (though I haver never attempted a cam per your engine), I have used a full radial clamp... may be a split boss with external clamp is a possible mod for you? On a generator, where the torsional oscillation comes from the engagement and disengagement of magnetic poles, I used an Olive on the shaft - double taper shape - clamped with a simple nut that screwed onto the hub of the rotor, to clamp the rotor onto the shaft. Simply, tapered plugs etc. Provide a full radial clamp for friction to transmit the torque from shaft to rotor..... whereas a grub screw tries to do the torque transmission on a tiny contact point.

Hope this is some use?
K2

 

[Weldsol]

Yep Unbrako
https://unbrako.com/wrenches.html

 

[ajoeiam]

I use a lot of #8 grubscrews on my engines, especially to hold the cams in place on the camshaft. I simply can't keep my 1/16" Allen (hex end) wrenches form rounding off when I tighten these grubscrews. I use "Bondhus" made in USA wrenches. Are there better quality Allen wrenches available, and if so who makes them. This issue is driving me crazy.---Brian

I have found similar problems even in using torx wrenches.

Wonder if you went to socket head cap screws (12.9 level of hardware) if you would have less issues.
I'd bet you can't get grub screws at that level though - - - - my guess is that many are a very low level quality - - - - not even 8.8 - - - it doesn't help things.

 

[Bentwings]

I use a lot of #8 grubscrews on my engines, especially to hold the cams in place on the camshaft. I simply can't keep my 1/16" Allen (hex end) wrenches form rounding off when I tighten these grubscrews. I use "Bondhus" made in USA wrenches. Are there better quality Allen wrenches available, and if so who makes them. This issue is driving me crazy.---Brian

Those have been long standing quality . If possible I’d switch to socket head screws . I intently hate grub screws set screws in the States. I’m currently working to convert to clamp hubs and clamp collars even if I have to make them special . I use two SHCS with these . They do take up more room so I have to make allowances . If you are careful you can make flats on the shaft. I had the same issue with stainless screws . Stainless is just too soft. It isn’t the tool that breaks down it’s the small hex in the screw in my experience .

 

[Brian Rupnow]

I think that in future designs, I will leave room for a #8 bolt instead of using a grub screw. The head of a #8 bolt will take a 0.141" wide Allen wrench, and can safely be turned down to 0.200" diameter. This will of course be somewhat clunkier looking, but at least the Allen wrench won't be stripping out and failing to secure the cam where I want it to be.---Brian

 

[Bentwings]

Be sure to put some kind of rust prevention on the screw paint maybe just oil flying around . These are usually pretty tough screws s I YHINK you have a good idea . A turned down head can split if you really get after it .

 

[peterl95124]

interesting to read all the negative comments about Bondhus, I on the other hand have only ever used Bondhus and only had one wear out after 20 years and literally thousands of screws tightened and untightened (the one for #2 hex socket head cap screws, of which the model Merlin has literally hundreds), but I keep both ball end and straight end drivers on hand and try to only use the ball end when necessary as its obvious that the straight end have more contact and last longer and have more torque capability. and the worn out ball end has been ground off and now I have a straight end that should last for the rest of my(!) lifetime.

I'd say if you are stripping your driver then you are over tightening your setscrew, if your setscrews are coming loose consider grinding a divot in the shaft where it contacts so the screw acts like a key and it can't slip, and then use "loctite thread sealant", not "thread locker", to keep the setscrew from coming loose (the "sealant" makes an easily removable grip, while the "locker" can require heat to remove). Consider the fact that "Weldon" shanks on end mills have a flat milled into them for a setscrew, because without the flat there's no way to get enough friction from a setscrew to keep a shaft from slipping. This is *especially* true for flywheels, they should be keyed, and the setscrew should only be there to keep the wheel from sliding off the shaft.

 

[petertha]

Peter, you raise a good point about Bondhus & would certainly clarify my statement if it came across as brand negative. For many years Bondhus was the only brand I used (and still use). Up until experimenting with some others, mostly metric & mostly driven by limited accessibility to their extensive catalog offerings as a function of where I live. I'm certainly am not implying they are bad, I just meant not significantly different than other 'good' options out there. And I am also a self confessed tool-a-holic. That has benefits beyond inventory though, the family has been trained to use THESE old screwdrivers to open lids, use as a chisel or stir paint <gasp>.

A few other discussion points. Anything I can say constituted 'wear' was quite honestly in the abuse range - a seized fastener by corrosion, Loctite, prior over-gronk whatever. Or incorrect tool insert angle under non-ideal conditions whereas maybe a non-90-deg angled hex would be a better choice (see Bondhus catalog). Or debris in the socket which reduces tool insertion/contact depth. Or prior fastener socket rounding by the last guy who was there, sometimes even me LOL. When I finally bothered to check, I was amazed at how little torque is specified for fasteners. 20-23 inch-pounds for #8 using this guide for example. Again, referring to Bonhus catalog, there is a whole assortment of specialty hex tools available we might not see at the walk in store or necessarily carried by suppliers. Some have upgraded metal or other refinements to the head geometry such as the ball ended hex tools. It pays to check around for the right tool for the job, but as humans we get impatient.

Also (trying to stay un-political here) tools, like many things these days, are a minefield. Many established brands are outsourcing but keeping the label. Some maintain the QC, others not so much. Some keep certain lines & import others. Bondhus themselves has apparently encompassed certain tools from Germany as below. And I'm also pretty certain that some loose Bondhus wrenches I bought actually came from the land of Henckels knives where the arms were backwards, or spelled Hencel or Henkel ... but I digress. I recently returned a Mitutoyo parallel set from an authorized Mitutoyo dealer that was not remotely close to their usual standards, very disappointing. Its a murky world out there.

https://www.engineersedge.com/torque_table_sae.htm
https://issuu.com/goblue42/docs/98700_rev_a_2021_bondhus_catalog_unpriced_web?fr=sYzllNjE0NTU0MzI
https://bondhustools.com/
Felo Tools has partnered with Bondhus for distribution rights in the US. They have been producing high-quality screwdrivers in Germany since 1878, and their lineup includes interchangeable screwdriver-blade systems, screwdriver sets, socket and bit sets, and specialty screwdrivers. Felo hand tools are the highest quality hand tools on the market; Felo simply doesn't produce low-end tools. These tools are designed for individuals who appreciate well-made tools and who need tools that work as designed.

 

[bluejets]

I use a lot of #8 grubscrews on my engines,

We don't tend to use #8 or any other American based sizes here (moreso metric) however I did notice one supplier showing the next size up allen key for a #8 grub screw.
Perhaps an answer there..?
#8-36 TPI UNF Fine Plain Black Uncoated Grade 14.9 Cup Point Socket (5/64" Key) Set Screws Grub ANSI B 18.3

Plus also this at the risk of saying how you should suck eggs.....
Everything You Need To Know About Grub Screws | RS

 

[Steamchick]

Gents, I reiterate that anything with torsional vibration, such as cams, flywheels, etc. should be secured for transmitting the torque by something HUGE (In torque transmitting ability) compared to the torque transmission qualities of a grub screw. I.E. a Tapered locking device, Key etc.
A cam has torque in one direction when it is working against the valve spring AND the Inertia of the valve AND the friction of the system. - The INERTIA OF THE VALVE IS USUALLY THE LIMITING FACTOR AT HIGH SPEED. Then after the valve is fully opened, the spring reverses the torsional loading on the shaft as the follower "slides down the hill".
This torsional vibration is a fatigue loading of 1 cycle per revolution, so at 600rpm you have 6000 cycles of fatigue loading on the point of the grub screw and surrounding tiny indentation.... Is it any wonder the grub screws cannot hold the cams in position? Just consider the damage a hammer drill used with a centre pop would make of the steel of the shaft if you did 10 minutes of work on it?
Grub screws are just not suitable BY DESIGN for this job.
Oh, and I have witnessed that in most cases where I have seen grub screws used "wrongly" the shaft is damaged so it is difficult to remove the components afterwards. That is a bodge, not good design. QED.
If you "get away with it" with the best screws and keys, then good luck to you.
But please don't spoil the many hours of excellent work on your models with poor design decisions, use the best you can... Surely that is the objective of this discussion site?
K2

 

[Peter Twissell]

K2,
While all you have written about grubscrews and cams is correct, have you calculated the magnitude of valve train loads in a model engine?
The scale factor is cubed for the mass of the parts and squared for the acceleration of those masses.
I have seen lawnmower engines, many times the size of our models, with plastic camshafts - and they last!
Brian's builds have demonstrated the grubscrews are adequate for his applications at this scale.

 

[ShopShoe]

This post is a possible deviation of the thread:

Excuse me if I'm getting too far off with this.....

Brian, I admire your skills and follow your builds. I would not want to misunderstand what is going on or put thoughts in your head or words in your mouth.

I think Brian works through a design-and-build with parts on shafts using grub screws or set screws to allow adjusting the timing and setting of parts on rotating shafts as part of the build. After things are finalized, then maybe somehting else is called for.

Perhaps there is a method that provides an adjustable feature with more security than the set screw, or is there an improved way of 'set-screwing" the connection. I would be interested.

A keyed connection would be less likely to spin or slip, but would not have the adjustability wanted for fine-tuning. What is the best of both worlds?

--ShopShoe

 

[Lloyd-ss]

We can usually "feel" when an Allen wrench is about to strip, whether it be the wrench or the hex hole.
We stop and grind a bit off the tip, being careful to not overheat it.

Here's an old trick I use. If you have some coarse paste lapping compound, dip the tip of the allen wrench in it and the abrasive will add just enough grip to get the screw adjusted.

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Maybe 30 years ago I bought a teeny squirt dispenser of Grip Doctor in the Craftsman tool section at Sears. It worked like a charm. Years later when it ran out I realized I had a whole can of the stuff with my other "chemical" supplies.