PDA

View Full Version : How do you broach a square hole?



RichTes
12-21-2009, 01:26 PM
I know the drill, oil, press part. How do you align the broach? It's not like the mill where you can move the table back and forth to align it.

Best I've been able to do is a groove in the bottom of a v-block clamped to the table and a bar with a tab on top to align the holder on the press.

Thanks,
Rich

tyrone shewlaces
12-21-2009, 01:35 PM
Could you use a little bitty end mill (say 1/16") to make a shallow square at the top of the hole to give the broach a start? Don't know if that will work, just the first thought in my head.

dp
12-21-2009, 02:06 PM
Do you mean clocking the broach in the hole, or knowing where the center of the square hole will be when finished? Those things follow the line of least resistance so it's imprecise as to the latter.

RichTes
12-21-2009, 02:55 PM
Take a boring bar, for example. I'd like the hole square to the bar. While the broach might want to drift, I'd like to at least start square.

The Dumont website says "The use of a ram adapter is advised with all
round, oval, D-hole broaches, and for square and hexagon broaches 1/4" and smaller" which is nice, but doesn't say how to get the adapter aligned.

Rich

Carld
12-21-2009, 03:09 PM
That is an issue I have not been confronted with, yet. There has to be a flat area at the top of the broach and you could use that with a machinist square to align it with the hole for the start. After you have pushed it in a little you may have to check it again but I wouldn't push it through in one stroke, I would check it several times until I felt good about how it was going.

This is an interesting question and I am interested in how others line up the square, round, etc broach. It's no problem with a keyway broach, it's self aligning.

Ken_Shea
12-21-2009, 03:24 PM
Rich,
This may offer some help, or not :)

http://bbs.homeshopmachinist.net/showthread.php?t=92

Carld
12-21-2009, 03:29 PM
Aw geez Ken, you gonna make us read through all seven pages for the answer?

Ken_Shea
12-21-2009, 03:30 PM
Aw geez Ken, you gonna make us read through all seven pages for the answer?

chuckle chuckle :D

oil mac
12-21-2009, 03:33 PM
Early on this year, i had to broach some weeny holes in brass, 1/8" square, This worked for me it was rough & ready, drilled out a portion of mild steel with a hole, through which the broach could slide, the corners of the broach bearing on the sides of the hole in this component (Component no 1)
Second used a portion of steel turned to dia of hole being broached, &upper part of this pin dia of hole in portion of steel which was going to be used to steady broach (component No1 )

Using pin to align component No1 to workpiece, clamp together, &squeeze broach through, after removing aligning pin This system i found kept broach straight &saved it deflecting &snapping

davidwdyer
12-21-2009, 03:37 PM
I have had the same problem, ie. lining up the broach.

What I tried to do was place a straight edge on the top side of the tool and eyeball it square with the cross piece of the press. This worked OK for what I was doing.

I have read that some machinists can square up a vise in a mill using a straight edge and lining it up with the back of the table. Some say they can consistently get within .002" every time.

I too am interested in a "real" solution for "clocking" the broach.

dp
12-21-2009, 03:45 PM
Clocking a square broach can be done with two machinist's squares. One body is gently clamped to the broach and the body of the second aligned to the blade the first and its blade aligned to the bar to be broached.

Carld
12-21-2009, 03:58 PM
:confused: Uhhhh, I looked at and read the 7 pages but found no help for him and I need another adult drink now.

I have an arbor press with a round ram and I guess if I had to do a square or round broach I would make an adapter to fit over the ram to hold the broach and the work would self align under the broach with a little care BUT, there has to be a better way. I guess it's off to the Dumont site for me but first I need a drink.

davidwdyer
12-21-2009, 04:13 PM
dp

I kinda get the idea, but could you send a pic or drawing.

I know it's a lot of trouble, but I know I will be broaching a square hole again soon.

Carld
12-21-2009, 04:47 PM
To whom are you directing this question/request?

lane
12-21-2009, 06:45 PM
I broach lots of square holes and just line broach up with a small square . Even hex holes too.

davidwdyer
12-21-2009, 07:01 PM
To whom are you directing this question/request?


I believe I was directing it to someone named "dp."

MaxxLagg
12-21-2009, 07:02 PM
Just drill it ;)

http://upper.us.edu/faculty/smith/reuleaux.htm

http://toolmonger.com/2006/11/30/tool-tech-square-drill-bits/

davidwdyer
12-22-2009, 05:53 AM
That drilling looks interesting. Someone was really thinking outside (or do I mean "inside"?) the box.

Broaches are expensive!!!

Where can these drills be purchased and how much do they run?

RichTes
12-22-2009, 06:06 AM
Going back to my original question, it would seem easier to align the square hole drill since you can do it on the mill and use the mills movements.

Have to look at that more.
Rich

Mcgyver
12-22-2009, 06:49 AM
I broach lots of square holes and just line broach up with a small square . Even hex holes too.

i'm guessing align means either making sure the resulting square is correctly positioned, ie that the sides of the square in in the right radial position.....or does aligned mean the broach is starting straight up and down?

if the later, its obvious how checking with a square works, but if the former i'm foggy on it? the broaches i have are round at the bottom so radial position of the square is determined by some bits of metal half a foot above the work surface. something like an angle plate aligned to an edge of the work and then a square on the angle plate up at the top of the broach (where the broach is square) would work...is there an easier way?

I've just eyeballed in the past, or if it mattered started the broach with hand pressure on a flat surface (plate or milling table) with things positioned such that the broach is horizontal so it is easily checked with a square...then off to the arbor press


Broaches are expensive!!!

make them! :)

oldtiffie
12-22-2009, 07:42 AM
Take a boring bar, for example. I'd like the hole square to the bar. While the broach might want to drift, I'd like to at least start square.

The Dumont website says "The use of a ram adapter is advised with all
round, oval, D-hole broaches, and for square and hexagon broaches 1/4" and smaller" which is nice, but doesn't say how to get the adapter aligned.

Rich

I am at a bit of a loss here.

Is the task to use a broatch to make a square hole or is it just to make a square hole with broatching as an option?

If the square hole is in a boring bar for a square HSS tool bit, the size and "squareness" are not at all fussy as any "out of square" etc. can be countered or corrected when the tool is being (off-hand?) ground.

It is were me, I would not even consider a broatch.

I'd just mill a square groove in the end of the boring bar to suit the tool bit and then silver-solder a "cap" onto the end of the boring bar to complete the fourth/last side of the square hole and then drill and tap the "cap" for clamping screw/s to suit.

A square broatch should have a round "pilot" to guide it into the hole.

A broatch when pressed in is very slender column which can fail catastrophically with no notice if the column height to width ratio is too high, and/or the load is too high and/or if the load is too eccentric to the broatch neutral axis and/or if the broatch is not aligned to the press ram centre/axis and/or the flat end of the ram as these will cause significant bending in the broatch.

This is why in commercial work that is geared-up for the job, the broatch is "drawn" (ie "pulled") through and is a lot less liable to fail under tension than it would if it were under compression when being pressed or pushed through.

I agree with Mcgyver as its not all that big a job to make a broatch out of "O1" (US and Canada) - aka "Silver Steel" in the UK and OZ.

For column conditions and states under load load see:
http://en.wikipedia.org/wiki/Column#Equilibrium.2C_instability.2C_and_loads

From:
http://en.wikipedia.org/wiki/Column#Equilibrium.2C_instability.2C_and_loads

Carld
12-22-2009, 09:24 AM
The problem as I see it and the OP saw is alignment to keep from breaking the broach or broaching off center.

I suggested using a holder on the end of the ram and in fact that is what Dumont says and in this link http://www.dumont.com/procedur.html it shows how.

Since I know how easy it is to break a push type broach I would make a holder to correctly align the broach with the table and part in the arbor press.

dp
12-22-2009, 09:45 AM
I am at a bit of a loss here.

Is the task to use a broatch to make a square hole or is it just to make a square hole with broatching as an option?

I took it to mean he'd like to find a way to align the broach so that the square hole is perfectly aligned with the centerline of the bar. I presume, as is typical of boring bars, that the hole at one end would be perpendicular to the centerline, and that the sides would be parallel to the centerline. The broach will more or less follow the hole in a least resistance path if things are reasonably aligned at the beginning of the push. Clocking the broach so that the sides are parallel to the centerline is a bit more of a trick which is why the machinist square was suggested.

Paul Alciatore
12-22-2009, 10:40 AM
I haven't done any square hole broaching, but I would wonder if the broach would have any tendency to follow the drilled hole like a reamer would? Just relax the driving force several times during the stroke to allow it to assume the position it wants under the press instead of forcing it sideways.

dp
12-22-2009, 10:53 AM
I haven't done any square hole broaching, but I would wonder if the broach would have any tendency to follow the drilled hole like a reamer would? Just relax the driving force several times during the stroke to allow it to assume the position it wants under the press instead of forcing it sideways.

That's the way I've always done it as I have never had a decent broaching station. It is surprising though how quickly thin broaches will bend and snap!

oldtiffie
12-22-2009, 04:04 PM
I haver still not seen any reply as to whether broatching is absolutely required or whether it is just an option for fitting a square tool-bit to a boring bar.

My next question - which I deliberately did not ask earlier - is that if the requirement is ONLY to fit a tool bit into a boring bar, then why not use a round (presumably HSS) tool bit when a square is not required - just a plain drilled hole to suit around boring bar.

Round tool bits (precision ground) are pretty cheap - especially down in the 1/8" > 3/16" > 1/4" > 5/16" > 3/8" areas. The smaller the better.

A round tool bit can be rotated in the boring bar to adjust front clearance and side rake on the tool.

A round tool bit will easily and effectively fit into a square hole.

RichTes
12-22-2009, 05:10 PM
Broaching isn't required, but I was playing with a boring bar to see if I could broach the hole square to the long axis as well as vertically.

A boring bar was for practice. Figure I could make a bunch of different sizes. Or just make the same size till I get it right!

Rich

Carld
12-22-2009, 05:58 PM
The boring bars I make just have a round hole in them that fits the size of square cutter over the diagonal corners. Square broaches are to expensive for stuff like that.

I have even filed a hole square a few times.

Rich Carlstedt
12-22-2009, 06:46 PM
To "square " the broach to the work, you take your pocket scale, with the spring clip on it, and place the scale horizontally on the broach with the spring clip grabbing it from behind. The scale will register on the flat of the broach and amplify the orientation of it. Then turn the broach to meet requirements.

Yes Paul , as soon as the broach enters the hole, you need to check it with a square on front and side, and backoff a few time when driving it home to allow it to compensate for angular error......or SNAP !

For broaching boring bars square,, You generally drilled them out a bit larger, and then sharpened a tool bit square (ended) and very sharp, and drive the tool bit right through the bar. As long as you are not trying to cut along all edges, it works.
It also helps if you have an undersized toolbit and use it first.
For a .250 " bit, I would use a 5/16 drill (. 312)
The diagonal measurement for a .250 bit is .365, so the meat left, is more than adequete to handle the tool bit in machining aplications.
If you want a real square hole, use the above application but start with smaller cross-section bits and work up
Rich

Rich

Rich Carlstedt
12-22-2009, 07:00 PM
To make a square broach, check out my method , using a belt sander (marks on the table) a 5-C collet block and a broken endmill.
The broach shown here is not square, because it was used for slotting


http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/BroachingPC270071-1.jpg
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/PC270068-1.jpg

This is a square corner broach made from a tap
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/BroachingTools.jpg

I also sharpen broken taps and use one corner. The photo shows the tap on the right side
This is neat for starting in a round hole and "indexing" to get each corner

Here it is cleaning out a Round corner...compare it to the other corners to see what its doing
This is done in a bridgeport with .001" moves per stroke

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/MiddleBearingShaping2.jpg

Rich

Rich Carlstedt
12-22-2009, 07:04 PM
How about a .040" square broached hole " ( miniature wrench)
here you see it. The broach broke , but I left it in the picture so you can see the results. The cutting tip was removed, it did not have enough clearance.
I grind all my broaches by hand

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/PB100019.jpg

Her is how you get allignment --simple huh ?
Normally the spring is on the back, but I shot this to show it gripping the broach.

Just put the scale on the important edge !

http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/Broachingmonitor1463.jpg

Its lots of fun guys

Rich