A couple years ago, I made a very quick and dirty rotary broach for a project i was working on in my normal job

it worked for the purpose it was intended, but i wanted to make an improved version.

the new version , i envisioned was precise, robust, and economical.

(i priced out a manufactured rotary broach similar to the size i'm constructing, it was over $500 USD)

last week, i took up the gauntlet, to make my vision a reality (and for a lot less money;))

as an added challenge, i'm going to do this project ,with only the stuff i have lying around the shop :grin:


ACT 1: The Capsule

after hunting down the materials, i decided to draw a plan for the capsule

the capsule is a sub-assembly of the rotary broach.
the capsule contains the toolholder shaft, roller bearing and thrust bearing assemblies, and their spacers and retainers.
it is designed to be taken apart for easy bearing changes, as necessary.
enjoy!

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i had [3] 6202-2RSC316MM ball bearings, and a needle thrust bearing in the shop, so the capsule was built around those specifications.
[side note: 6202-2rsc316mm is a special bearing, the outside and thickness are metric dimensions, the ID is imperial]{also, the bearings are 316 stainless}

the broach holder was constructed from .875" hexagonal unknownium steel stock to a finished length of 2.750"
3 grooves were added to the broach holder for bearing retention by 5/8" external snap rings
i constructed 3 spacers from aluminum to provide extra clearance between the ball bearings

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the main part of the broach holder shaft was turned to .625"
the distal end of the broach holder was turned to metric dimensions 14.9mm for a distance of 4.7mm, to accept the needle thrust bearing (27.8x15x4)
the proximal end was drilled to 7.5mm and then reamed to 8mm
then the broach retainer screw was added, i drilled and tapped for a 1/4-20 x 1/2" set screw

here is the capsule fully assembled

290971290970
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Stay Tuned for Act 2...... (if you dare)
 
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I think you will have to mill the 1 deg angle on the base and then have an additional offset to get the tip of the cutter on center. This will be an issue if you have cutters of different lengths. No?
Robert
i'l be interested to see if cutter length is critical.
the thought was to make the cutters to the same general length for grinding purposes,
but i had not considered the ramifications for length yet :bang head:
 
ACT 3: Drilling,Tapping & Milling

Now, the capsule fits like a glove into the carrier,
but i need to drive the carrier and put a 1° angle on the carrier
and i need to drill and tap for 3) 1/4-20 socket head capscrews in a 1.5" bolt circle

i chucked up and indicated the carrier, gave it a scratch at 1.5" to aid in bolt center location

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i needed to make the driveshaft to make the whole thing work, so i sketched out the idea-
then i made it! :big grin:


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i transferred the bolt circle onto both the driveshaft and the carrier
and used a pair of dividers to walk out 3 equidistant points on the carrier, on the 1.5" mark
i punched the first divot and walked out the other 2 points, until all 3 were the same distance and on the 1.5 mark.
i went through the same process on the driveshaft.
it was quick work and i didn't have to use a lot of tools get there

the pilot holes for both the carrier and driveshaft were drilled then punched out to .185" in the old South Bend drill press
the carrier was drilled to .201" to a depth of .395"

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next came the milling of the carrier!

i set the carrier into the Bridgeport's vise with a v block and a 1° angle block under the work.
i milled the carrier approximately .030" to ensure the 1° was transferred across the whole face of the carrier.

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here is a shot after milling
the carrier was tapped to 1/4-20 to .375" depth
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i reassembled the carrier and enlarged the driveshaft thru holes to 7mm for clearance

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act 4, coming soon..... same bat time, same bat station
 
UD, do you have that 3/4” tail shaft on center???? And the 1° on the back of the body??? And everything else is made to be on center??? Sorry UD, to me things don’t look right??? Unless I’m missing something the design will have a problem. VERY IMPORTANT BELOW.

“When everything is made and you have the rotary broach set-up to use………The broach tip (cutting part) MUST BE ON CENTER. And yes, broach length is critical when and if you interchange them.”
 
I assumed you were going to use this in the lathe tailstock with the work rotating. I believe that could work if you get the cutter on center. If you use this in the mill I feel like the cutter will just move in a circle and never be on center? I have never used one of these personally. Am I missing something?
Robert
 
UD, do you have that 3/4” tail shaft on center???? And the 1° on the back of the body??? And everything else is made to be on center??? Sorry UD, to me things don’t look right??? Unless I’m missing something the design will have a problem. VERY IMPORTANT BELOW.

“When everything is made and you have the rotary broach set-up to use………The broach tip (cutting part) MUST BE ON CENTER. And yes, broach length is critical when and if you interchange them.”
Hi Chips,
to recap...
the driveshaft was turned and faced after it was constructed in a ER32 collet system in the spindle of my lathe (sub .001" indicated runout)
the 1.5" bolt circle was inscribed with a boring tool
the carrier was bored internally in a 4 jaw independent chuck (indicated sub .001" runout) and i turned the od in the same set up
the carrier was reversed and re-indicated and faced.
the 1.5" bolt circle was inscribed on the face of the carrier
after locating, drilling, & tapping the 3 mounting holes, the rear of the carrier was milled at 1°
the driveshaft was drilled to 7mm on the 3 bolt holes, to allow clearance and minor adjustment, if truing is necessary.
considerations have been made to enlarge the mounting holes if the carrier needed it.
 
FINAL ACT: ASSEMBLY
i finished assembly and took some pictures...

IMG-3316.JPG

IMG-3315.JPG


View attachment IMG-3323.MOV
















there is no tool in the holder, i substituted a 3/8" ball bearing for testing purposes
this is only a test!

when i made my down and dirty broach, i made no attempt at accuracy in any sense of the word.
i banged it out in less than an hour.
nothing was on center, nothing was Book of Hoyle about it, there was no consideration of tool length
the tool was hacked out of a new tool blank to provide about 10° side clearance (poorly made at that)
it was an abomination that got the job done.
from the experiments of the former, i learned not to fear the rotary broach
nor the construction of a better one.
for right or wrong, here is the rotary broach as i made it.

rotary broach drawing.jpg

i'll do testing and broach fabrication.
i'll share my findings as i go.

thank you for reading, watching and being a part of the experience.
 
FINAL ACT: ASSEMBLY
i finished assembly and took some pictures...

View attachment 291357

View attachment 291359


View attachment 291360
















there is no tool in the holder, i substituted a 3/8" ball bearing for testing purposes
this is only a test!

when i made my down and dirty broach, i made no attempt at accuracy in any sense of the word.
i banged it out in less than an hour.
nothing was on center, nothing was Book of Hoyle about it, there was no consideration of tool length
the tool was hacked out of a new tool blank to provide about 10° side clearance (poorly made at that)
it was an abomination that got the job done.
from the experiments of the former, i learned not to fear the rotary broach
nor the construction of a better one.
for right or wrong, here is the rotary broach as i made it.

View attachment 291361

i'll do testing and broach fabrication.
i'll share my findings as i go.

thank you for reading, watching and being a part of the experience.

Looking forward to seeing test cuts, results and photos of the parts made! Nice job Ulma!


Sent from my iPhone using Tapatalk
 
OK UD, if everything is on center and you have induced a 1° angle. And if you have no provisions for an offset. Then sorry, but the broach cutting end will run in a solid angle pattern and not remain stationary as it should be…Dave.
 
When the cutter is stationary. The 1° angle makes the stationary cutter end walk around on a small angle causing a minut shear action every rotation. If the cutter end is not stationary but instead doing a solid angle pattern thing. I have no idea, probably wild stuff will happen, please be careful.
 
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