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Thread: SHS Broaching
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26th Apr 2021, 11:25 PM #1Golden Member
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SHS Broaching
After a number of months out of the shed I finally made a brief start on my weld table project (I will try and run a thread in the projects section). After stripping off the horrible blue paint I quickly came across my first issue. I had designed it such that the table height can be adjusted via a 65mm SHS sliding inside a 75mm SHS. Either due to poor calculations or manufacturing tolerances they do not fit. From memory I had a 75mm x 4mm SHS outer and 65mm x 2mm inner so there should not have been an issue (and it is not just the weld seam causing the interference). i will remeasure the tubes but rather than buy another size I want to try to broach out the 75x4 tube slightly larger. I only need to take around 1mm or less out side to side. Each of 6 SHS are 600mm long.
Having previously watched the Fireball Tool method of removing weld seams I was thinking about something similar to broach out my tube. What are your thoughts on a broach similar to this;
SHS Broach.jpg
The dimensions are not yet firmed up other than the first and last cutter being 1mm difference in width in order to cut out the required metal. Due to the tube length I would propose sizeable gaps in the cutter to capture the swarf without binding. Due to the surface area being cut I would expect it would require multiple cutting edges such that each only takes a small amount. Material wise I am not sure and am open to suggestions. I have plenty of 4140 that I could try to harden and temper. I could try to get fancy and attach tool steel to a mild steel core (sounds complex). It could all be cut on the mill.
I would most likely pull this through the material using maybe M20 all-thread. My press is of the small chinesium 12T type and might not be suitable.
Am I off with the pixies on this one or do you think this is feasible? Maybe I am over-complicating my life for the sake of buying alternate SHS. To harden anything I would need to make a heat treat oven although that is a planned project anyway.
Thoughts?
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26th Apr 2021, 11:33 PM #2Gear expert in training
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Stupid question...instead of trying to clean up the inside of the large tube, why not just mill/grind down the outside of the small tube so it fits?
EDIT: I definitely think you're over-complicating your life for $50 worth of new material
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27th Apr 2021, 12:01 AM #3Most Valued Member
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I’m known for doing some things the hard way, but even I would go buy some 3mm wall.
The cost in time and material to make the broach will waaaaaaaaaaay exceed the cost of new tube.
On a 75mm tube over a shortish length like that you can hose clamp a die grinder to a steel rod, sounds sketchy but for the most part it’s not too bad, the angry bit is largely contained in the tube.
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27th Apr 2021, 12:23 AM #4Golden Member
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I guess I knew the answer but needed to hear it from others lol
Will order more steel tomorrow.
Elan - if I ground down the OD of the internal tube I would need to redraw everything (not hard I just don't want to)
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27th Apr 2021, 06:21 AM #5Most Valued Member
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You would need to apply incredible force on a broaching cut that big. You are in 8' cheater bar territory. And 4140 would never do the job. Hss blanks would be needed and probably about double the teeth on your broach.
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27th Apr 2021, 07:56 PM #6Golden Member
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New metal ordered. Another hour of blue paint grinding ahead grrrrrrr
Why would the 4140 not have been any good as a broach? I have alot to learn about various metal properties!!!!
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27th Apr 2021, 09:56 PM #7Most Valued Member
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Oven cleaner to get rid of the paint.
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28th Apr 2021, 12:35 AM #8Most Valued Member
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I can't say 4140 would definitely 100% not work but HSS has some magical properties that cause it not the lose its hardness even when heated almost to red hot. 4140 even in its hardest possible state cant be treated so roughly and also just cannot be hardened as effectively.
If it made good cutting tools, cutting tools would be made from it.
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28th Apr 2021, 06:26 PM #9Diamond Member
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