1/8 Broach???

Remember that you're going to need shims that long too! The shims for the 2nd/3rd cut that come with the broach are only going to be ~3/4" long.

Also, as was mentioned above, that is a LONG cut for a broach. I'd be quite afraid that it would be too much chip load for the teeth. You might find value in backing it out/clearing chips about 1/2 way through the hole, particularly if the force require to push it increases significantly.
 
I did not give shim a thought, and thanks for the advice about clearing the chips. Once I get my set and start on it, will check see how it feels and maybe do what Projectnut did work it from both ends. Being brass maybe that will help being little softer than what steel would be. I am going to research benmychree ideal about single point broaching on lathe. See what Erich and benmychree talking about gagging with chips since the gullets can only hold so much.
 
Kroll said:
I did not give shim a thought, and thanks for the advice about clearing the chips. Once I get my set and start on it, will check see how it feels and maybe do what Projectnut did work it from both ends. Being brass maybe that will help being little softer than what steel would be. I am going to research benmychree ideal about single point broaching on lathe. See what Erich and benmychree talking about gagging with chips since the gullets can only hold so much.
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Upon further consideration, I wonder if you could drill out or mill out a bunch of the material ahead of time, and just use the broach to do cleanup? That would help with chip load.
 
The shims for the "B" series broaches are .032" thick and .052" thick. Both are 1 3/4" long. The bushing sticks into the bore 1 7/16" with the shim extending 1/16" beyond the bushing. If you're cutting long keyways in anything harder than aluminum I would suggest at the minimum to take a cut about half the length of the broach, back it out, clean and reoil it and make a complete pass.
 
shims are easy to make, so make several of different thickness so you can make more passes with smaller cuts and chip problem will go away. you can double up shims ---just put the thinner one behind the thicker one. Dave
 
Dave Smith said:
shims are easy to make, so make several of different thickness so you can make more passes with smaller cuts and chip problem will go away. you can double up shims ---just put the thinner one behind the thicker one. Dave
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Thinner shims won't help; they only affect the number of teeth that cut, not the chip load of each individual tooth (which is the real problem).
 
no the shims determine the depth of the cut each time--smaller cuts will not have heavy chips that will not roll or break easily and eliminate the loading up.
 
Unless I severely misunderstand how broaches work, the size of the tooth vs the previous tooth determines the depth of the cut of that tooth. Which determines the chip load of that tooth.

ETA: It is the depth of the cut (determined by the design of the broach) AND the length of the cut (determined by the size of the material) that determines the chip load. The 1st is determined at manufacturing time of the broach, the 2nd is determined by the size of the material. All the shim does is change the total depth of the cut in relation to the bushing, which only affects the cut depth of the 1st tooth to make a cut (up to the manufactured size, as listed above).
 
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And of course the broaches are designed for a suitable load from tooth to tooth. Without the right shims, the first tooth will take the burden and potentially jam or have a problem. Once started, the chip load will be acceptable.
 
that is why the broaches are tapered so each tooth only takes only the correct amount it can handle ---there is plenty of space behind each tooth to handle each cut as long as you don't take too deep of a cut each pass---you decide how deep each cut is by the thickness of the shim, by adding thinner shims each pass eliminates chip load problem---that is why you need several shims while broaching, not just one thickness. Dave
 
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