Unidentified Set Screw

[sddutch]

I have a CNC engraving machine and one of the tools uses a tiny set screw to hold my engraving cutters in place. Recently the tiny set screw grew wings and launched itself from the machine to points unknown and I need to replace it.

It is 0.25 inches long, 0.125 inches wide, and has a cross "+" head. From what I have been able to find online, I think it is a number 5 set screw, but all of the ones I have been able to find have a 6 sided "hex" head and not the cross type that I need.

Can someone identify this set screw and tell me where I can purchase some (See attached .pdf document)?

Thanks.

 

[L Vanice]

That style of drive is called Bristol. You can buy sets of L-shaped Bristol wrenches from the usual industrial tool sellers. I have not looked to see if the screws are available, but now you know what to ask Google.

Of course, the threads and other dimensions would be the same as a hex head version of the screw, which would be much easier to find locally. You could even use Google to search for engraving machine supplies sellers, who would likely sell the OEM screws for a New Hermes or whatever brand of engraver you have.

Larry

 

[awander]

Sorry, but I just have to ask-why can't you use the set screws with the Allen (six-sided recess)

That style of drive is called Bristol. You can buy sets of L-shaped Bristol wrenches from the usual industrial tool sellers. I have not looked to see if the screws are available, but now you know what to ask Google.

Of course, the threads and other dimensions would be the same as a hex head version of the screw, which would be much easier to find locally. You could even use Google to search for engraving machine supplies sellers, who would likely sell the OEM screws for a New Hermes or whatever brand of engraver you have.

Larry

head?

 

[L Vanice]

Bristol sockets are stronger and much less likely to strip out than Allen (hex) sockets. The engraving machine companies knew that and used the Bristol screws for the cutters because the screws had to be loosened and tightened repeatably in normal use.

If available, Torx head set screws would be a good replacement for the Bristol screws.

Larry

 

[awander]

Bristol sockets are stronger and much less likely to strip out than Allen (hex) sockets. The engraving machine companies knew that and used the Bristol screws for the cutters because the screws had to be loosened and tightened repeatably in normal use.

If available, Torx head set screws would be a good replacement for the Bristol screws.

Larry

Makes sense, thanks

 

[technocrat]

note that there are 4 and 6 spline bristol

 

[L Vanice]

note that there are 4 and 6 spline bristol

Here is a table showing that any given thread size has a fixed number of splines. No. 5 has only four splines.

Bristol Screw Sets

Larry

 

[jim rozen]

WW2 aviation electronics use those spline wrench setscrews. If you happen to be a kid trying to convert an old Command set for ham radio use, and are trying to drill one of those out with an eggbeater drill using hardware store drills, trust me it does not go well. Those setscrews are harder than bill-goat dicks.

 

[EPAIII]

If you are still unshure of the thread size, just try some regular screws (Ace Hardware) in the hole to see what matches. Then you can buy the, probably expensive, Bristol head screw in that size.

 

[boslab]

Never encountered Bristol screws in the wild bar once, and they were holding a C60 source in a gamma source, I don’t suppose they wanted people tinkering with that! So it was a kind of security screw,
Mark

 

[GregSY]

There are really two issues here, and they are not tied to one another. The OP asked for the screw he 'needs'. That would be the screw with the proper thread and to a lesser extent, length. The thread should be first be identified, then the second issue - the type of drive - can be included in the hunt.

A regular Allen head might not be 'ideal' per the designer's directive, but would be way better than the existing Bristol screw which is MIA. So...you buy a box of 100 Allen heads from McMaster and get back to work. Then, as time goes by and the Allen's fall victim to flinging and stripping, you have time to find the Bristol screws and wait for them to arrive from, well, Bristol.

 

[jim rozen]

Aside: cobalt 60 source: nuclear orientation thermometer? Did you work for Oxford?

 

[John Garner]

I've encountered internal-spline-drive setscrews under both "Bristo" and "Bristol" labels, and L-shaped splined drivers for both "Bristo" and "Bristol" setscrews. Anyone here know the story behind the different but oh-so-similar names?

 

[Dan from Oakland]

McMaster Carr sells spline drive "hex" wrench sets.
I have a hurco that uses spline drive set screws to attach encoder discs, and MCM was the only place i could fiind the really small sizes.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[James H Clark]

To determine what thread you have, you need find out what the minor diameter of the threaded hole is. Then turn a small hardwood dowel to a size a few thousandths larger than the threaded hole. Then screw the dowel into the hole and back out. You can determine the thread markings on the dowel. I usually blacken the dowel before screwing it into the hole.
JH