# broaching



## MHW20 (Dec 18, 2019)

Hi I need to broach a 1 inch square hole 2 inches deep it is a thru hole . Where is a place to get affordable broaches


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## Tom O (Dec 18, 2019)

That would take a lot of coin to buy something like that I bought a 1/4” square one I think it was around $80.00 you would be better off making one.


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## MHW20 (Dec 18, 2019)

yes contemplated that was looking at rotary broaches there just as expensive but look easier to build


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## francist (Dec 18, 2019)

I’m thinking in addition to big dollars it’ll take some pretty big muscle to push a 1” square broach through 2” of material regardless of what type of broach. That’s a pretty serious hole.


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## MHW20 (Dec 18, 2019)

ya looks like 9 ton on the chart my press will do it but have to go slow or break broach looks like even Rotary broachs take a lot of pressure


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## YYCHM (Dec 18, 2019)

Would milling the square out and finishing the corners with a file or broach be an option?


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## MHW20 (Dec 18, 2019)

yes drilled out to 15/16th so far just thought it mite be easier rotary broach and then have another tool lol


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## GrayTech (Dec 18, 2019)

Drll 4 smaller holes in the corners and file the rest?


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## YYCHM (Dec 18, 2019)

What are you building?  Maybe there is a whole different approach that would accomplish what you're trying to achieve.


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## Dabbler (Dec 19, 2019)

rotary broaches take little pressure.  each corner cuts independently.  There is also a slight slicing motion on the sides similar to scraping.  They cut very slowly but need little pressure.  I'd guess that 1" would be about .010 per minute. but that broach would cost $$$$...  The cut would take 90 minutes to 2 hrs.

instead of going to the final answer, I'd cut a 1" hole with a twist drill, then plunge cut with progressively better holes by plunging with centre cutting end mills, 1/2" and 1/4" .  If I were doing only one hole in mild steel (you didn't specify the material) then I'd be inclined to make a carbide chisel and 'scrape' the rest: probably an hour or 2 to finish it. (HSS will do as well, especially if you have a 1/2" blank - it will require sharpening every 20 minutes/80 cuts or so)    Cleaning up the corner takes the longest time.  You can use a medium soft hammer to drive the cutter.
.


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## PeterT (Dec 19, 2019)

Just curious, what are you making? Can the part be 'built up' instead?


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## YYCHM (Dec 19, 2019)

Drill her out and weld a piece of square tubing in there?


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## Dabbler (Dec 20, 2019)

John N had a great idea for a hardy hole, but his would work for you as well.  

Get a 1" drive socket:  You can even pick them up used cheap, as few want them.  Drill  a clearance hole, and then counter bore the hole for the socket so it is just below the surface.  weld it in, and grind off the excess.  a cheap drill, a boring head (if you have one or can borrow one) and a welder is all you need...


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## sanderzTM (Dec 20, 2019)

> That would take a lot of coin to buy something like that I bought a 1/4” square one I think it was around $80.00 you would be better off making one.



50 dollars, not more.


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## YYCHM (Dec 20, 2019)

Dabbler said:


> John N had a great idea for a hardy hole, but his would work for you as well.



Who is John N?


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## Dabbler (Dec 20, 2019)

oops:  johnnielsen.  When all the 'johns' get toghether we refer to eachother as 'john A' john C' 'john N', etc.  It seems quite silly to say 'hey, John!  and have everyone look.


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## PeterT (Dec 20, 2019)

That's a bit of metal to remove. Depending on what what exactly you are trying to achieve, like modifying an existing plate for some purpose vs. making something from scratch, how accurate the surfaces need to be, surface finish, how strong etc..... maybe there is an alternate technique to build it up from smaller sub-components & either bolt together or weld. Here is example sketch using 2 parts where the slot could be milled yielding 3 of the 4 surfaces. Or you could make it out of 4 blocks with surfaces just face milled. Food for thought


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## Tom Kitta (Dec 20, 2019)

Drill the hole. If you have a shaper and proper attachment cut it out square. If not, drill the hole anyways and using small endmill remove extra material till you have small round corners and manually square it. 

I usually cheat and do a simple U shape on the mill and weld to it the top of U made of flat stock. 

You could also broach it with cheaper and commonly available brioches for key making but you would have to build a jug for that. 

If this is some soft metal like aluminium you could use lathe as manual shaper. Not sure i its worth it with 2" of mild steel. 

Square broach in 1" size new would be 100s of USD - I would guess like $500+. https://www.mscdirect.com/product/details/00307645  and that maxes out at 2" of mild steel.  You may get used one for say $200+ - that is my guess as the biggest I saw were 1/2" - much more $$$ then just regular broach. Getting 1" HSS and making your own broach is also expensive as even short piece of 1" HSS blank is not cheap not to mention time consuming. If material is aluminium you could try using hardened alloy steel but still time consuming to make your own.


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## PeterT (Dec 20, 2019)

The only thing about end milling is the material is 2" thick working within a 1x1" pocket if I understood the dimensions. So an EM with that mount of flute length is probably going to be a larger diameter which leaves even more un-machined fillet in the corners to do my hand. Or if the corners are not critical, just the flats, then 4 holes could be drilled on the intersections. Well, I think more information would yield better possible solutions. So far we have discussed about 25K$ worth of machines. LOL


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## Tom Kitta (Dec 20, 2019)

I was thinking of milling it from both sides - so just 1 inch end mill stick out. 

He could drill on 4 corners a bit further out - i.e. place the drill center at the exact spot the 1" ends - if you can live with the "extra" 3/4 holes in the material. I think this is what PeterT means by at "intersections". 

For rotary broaching this would get ultra expensive and I believe the limit is only 1.5" not 2" - so maybe had to be done from both sides. Setup would cost AFAIK more then single square broach.

Getting someone else to cut the hole - i.e. farm it out could be an option.


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## eotrfish (Dec 20, 2019)

You could drill out most of the waste material then farm it out to a shop with a decent ram EDM.  Should be able to hold +/- .002” with perfect alignment and dead square corners.


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## historicalarms (Dec 21, 2019)

I think two 1/2" HSS square cutters ( 6 or 7 bucks each) to make a couple of "usable" broaches and then used side by each in the slot that needs to be cut in the alignment/guide shaft would work..at least that's how I would "frugally" attack a one-off that I may never use again. 

  Another "usable in a pinch" method I can come up with is to drill/ mill all the excess metal away as was previously mentioned but I would drill the pilot hole a bit deeper in the work-piece and mill past the 1" requirement of the opening then install the 1" key or whatever is being used in the slot and them tightly shim the backside of the cutout to tighten the slot to size required.


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## Dabbler (Dec 21, 2019)

Asking 5 machinists how to do something is likely to yield 10 or more ways  to do it...   If you ask an expert, the likely response is 'it depends'.


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## Everett (Dec 21, 2019)

Where do you live MHW20?  There are a few people with shaper/slotting machines around, you might find a local with one who you could horse trade favors with.  If I was to do something of a square hole that size that would be my first thought for machinery, but like a number of people have already said more information about material/purpose/etc would be helpful.


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