Building KEN I Rotary broaching tool

[coopertje]

Hi Ken,

I know what you mean about 3 jaw chucks, they normally are not that accurate. I was lucky and got a accurate one with the machine, too bad the outside jaws are missing.

Started with assembling the parts of the holder. Put bearing grease for the trust bearing

And mounted the broach holder with light tapping with a plastic hammer. I bought some shims to set the trust bearing to tension, I needed 0.6mm in total. Its running easy and there is no any play on the head

Tool finished!! Put the broaching holder in the tail stock and mounted a piece of 10mm silver steel in the holes. The total run-out is 0.02mm, not bad for a home made tool, I am happy! If I had took the effort to make a collet for drilling and reaming the 10mm hole it could have been even better….

Then I cutted 11 pieces (1 trial piece, hope 10 good ones) of 10mm silver steel and chamber them in the lathe on one side

And milled a flat surface on them, 8mm mill, 1mm deep

I decided to make a 6mm Hex broach, first made 2 parallel side so I could check the dimensions easily

During the machining I made a mistake by having the collet holder not flat in the vice, so now it will be a 5mm broach!

Here it is milled and I tried to harden it. Heated until red and dropped in a bucked with old motor oil. Then heated again until just becoming red and dropped it in cold water.

To bring the relieve I took my Clackson grinder and try to set-up the angle with a protractor (the grease on my jacked is just to make it water resistant). Its a great machine but a real pain to set-up angles accurate.

To get the broach back parallel in the collet I used a parallel and flat table (Tacchella bed), have the flat side of the broach on the parallel and tighten the collet

Then tried to grind the broach by pressing the collet holder agains a flat and sliding it up and down. At the second face I hit the stone with the tip…..so now it will become a 4mm broach!

Took the already finished dividing head of the Tacchella and bolted it to the Clackson table.

I set the angle by eye (big mistake, but I got impatient)….and grinded the broach. This worked out well. Here it is after grinding, and with a way to large relieve angle.

Chucked up a piece of aluminum and drilled a 4mm hole and gave it a light chamber. Put the broach in the tailstock and brought it in position with the 2 screws fixing the bearing holder to the MT3 shaft loose. Let the lather run on very low rpm and put some pressure with the tailstock. Switched off the lathe while keeping the pressure on the tool. Then tightened the 2 screws on the back, this should be center. This is the procedure described by Ken. Started the lathe and hold my breath. I was able to keep the tailstock moving in nice and steady. I checked several times if I was not pressing the tailstock backward, but no, the broach is CUTTING!

Put in an allan key and it a very nice and tight fit. My goal has been achieved, I drilled a hexagonal hole!

Then tried a piece of brass. It worked ok for the first 3 to 4mm and then the broach got rotated or damaged I think. Also the hardening did not worked out well, I guess with my method you just harden the surface and I reduced the size with grinding. The broach has now some rounded corners. Can it be an option to harden it after grinding?? So now this broach will become the 3mm version :big:

Thank you so much Ken for sharing your design, its a perfect tool and but a little but of practice and experience it work great :bow: :bow: :bow:

Thanks for watching, regards Jeroen

 

[swilliams]

This is really cool. Great stuff Jeroen and Ken. I think I'll have to build one of these

Steve

 

[kf2qd]

What was you material, and how did you harden it? Case hardening would be only on the surface, and could be ground off. If you used a quench hardening material the hard should go all the way through.

 

[Ken I]

Very cool Jeroen.

The broach was not hard enough - once the corners go it will jam as yours did.

Drill rod need to be heated to carrot red / bright orange (dull red doesn't cut it) and quenched - it comes in air, oil or water hardening grades.

I don't get why you heated it twice.

Ken

 

[arnoldb]

Good going Jeroen Thm:

If you want to temper the silver steel after hardening it, it must not get anywhere near red hot again; that will just anneal it and lose nearly all hardness.

After hardening and grinding it, gently heat it on the shank side with a torch, and keep a close eye on the ground end. You'll see the metal changing colour from the heated end - the colour will travel slowly toward the ground end. The moment the ground end turns a bit yellow in colour, stop heating and quench it again. This should give a good temper for a broach without softening it too much.

Kind regards, Arnold

 

[coopertje]

Hi Steve, you should build one, its a really fun project and most off all a very useful one!

kf2gd, I used silver steel (think its called silver steel in the USA). As Ken already indicated my fault is most likely the temperature, it was not hot enough for hardening. I need to get some heat resistant stones to be able to get more heat in the material, now I need to hold it with a pliers, sucking up part of the heat applied.

Thanks for the tip Arnold, indeed I was "Trying" to temper it after hardening.....

I will make a square broach just for testing and playing in the below mentioned sequence:

- Heat the tip until carrot red / bright orange
- Quench it in cold water
- Grind it to shape and dimension
- Heat again on the shank as described by Arnold

I will keep you informed about the results, thank you all for your comments and tips!

Best regards Jeroen

 

[swilliams]

One question. Will this work ok in a small lathe? Mine is 9" swing and weighs about 200kg

 

[Dan Rowe]

Jeroen,

I was going to suggest using a magnet to indicate the quench temperature but that method does not work for all alloys.

Here is a link to a blacksmith approach to heat treatment of carbon steel.
http://tidewaterblacksmiths.net/2.html

Dan

 

[Ken I]

- Heat the tip until carrot red / bright orange
- Quench it in cold water
- Grind it to shape and dimension
- Heat again on the shank as described by Arnold (to straw colour)

That's it Jeroen - since you heated it red on the second go around I presumed you were trying to reharden it - that would not be tempering - the way Arnold suggests is correct.

Tip: Don't use pliers for holding - wrap a length of wire around the shank and use that for "dangling" or pick up.

Swilliams - it will work on even the smallest lathe - power is generally not the issue - tailstock thrust is the limiting factor - I would guess your lathe would handle up to about 8mm AF Hex in mild steel.

Ken

 

[Don1966]

http://mikesworkshop.weebly.com/rotary-broaching.html
I have attached the above link for a rotary broach this will work on a small lathe for SWilliam. Great project Jeron I really enjoyed you work and your affords to show us how it is done. Thank you for sharing all your photos.

Regards Don

 

[swilliams]

Thanks Ken and Don, great stuff

Cheers
Steve

 

[steamer]

Jerone,

I would do just that with tool steel. Grind it and then harden! It only takes a very small rise in temperature to blow the temper of the steel with tool steels. Without coolant on the grinder...you'll blow the temper for sure. The part is so small, that I don't think it's going to distort much during quenching.

I would grind it, harden and then draw the temper to straw yellow.

Harden as others have stated. Wrap it in wire and then dip it in liquid soap. It will keep the scale down

POLISH the tool nice and bright....this is important for the next step!

Holding the tool vertical, heat the tool from the shank side and carefully watch the color...straw will appear pretty quickly near the back and start to climb up the part towards the cutting edge...The Cutting edge is all that matters!

When it gets to the cutting edge...immediately quench it in oil again. The shank will be blue and tough, while the cutting edge will be very hard but not brittle.

Spend some time honing the edges with a stone....then give it a try.

Dave

 

[coopertje]

Thank you for your response and help guys, I really appreciate it. I have some things to learn here, (accurate) tool making is a new dimension for me. Yesterday I visit a friend, he has a beautiful Shaublin 102. This thing is new, he had it send to Shaublin factory to have the machine re-grinded to original specifications. Digital readout system with a resolution of 0.5 micrometer!! He is able to make parts with an accuracy of 0.002mm. Damn, I was so happy that I could make parts within 0.01mm (tried better but without success). But is was very educational, first thing to do is get a more accurate dial indicator and start measuring my machine better. Then I know what I can expect out of my machine and what errors are from the operator (very frustrating when you try to achieve accuracies above machine specifications!). After that it will be playing time! When I get to that stage I might start a topic on this if people are interested.

Back to the broach, In the article mentioned by Don you see the drilled tip of the broach, I knew I have seen that before, did not remember where. According to Ken this is not necessary so I will safe myself the trouble of making it.

I do not know what grade of silver steel I have, some mention quench in water, some in oil. What would be advisable here, or does it not matter so much?

To Dave, would it be enough to polish (emery paper?) and after hone just the front side of the broach? I am a little scared about the hexagonal sides, do not want to make a radius on them when polishing and honing...

Thanks in advance for sharing your wisdom!

Happy machining, regards Jeroen

 

[Ken I]

The drilled point produces excessive rake (± 26°) unless you grind the drill point to a shallower angle - in any case the surface finish is generally lousy and I consider good finish more important for smooth chip flow. I have ground spherical depressions (good finish) to give different rakes - it does reduce the force very slightly - but as I have said before not worth the bother - it's far easier to get a good finish on a flat face. Additionally, raked broaches are weaker and more prone to chipping - especially with the "grooves" of a poor drilled finish close to the edge acting as stress raisers - that's just asking for the edges to fail quickly.

Use a flat face and live with the slightly increaced force.

You only need to polish the area you are interested in - in this case make it the flat face and watch the colour change on that although the sides give you a better view of the heat "creeping" towards the face.

It takes a lot of elbow grease to remove any significant amount off glass hard stock with fine emery paper - even on the corners - wrap the emery around a flat stick or file to avoid going around the corners. You need only "polish" one side not the entire hex.

Regards,
Ken

 

[coopertje]

You need only "polish" one side not the entire hex.

Just to be absolutely sure, with this you mean the tip (front side) of the broach. So I will not touch the grinded hex side with a stone....

Regards Jeroen

 

[Ken I]

Jeroen, You can do either.

If you are unhappy about polishing one side of the hexagon then you can do just the face.

The side of the hexagon works better because you can see the colour "creeping" towards the face as you heat the shank - as suggested by Steamer.

If you only polish the face you will have no idea of how fast the heat is coming towards it and it might change from straw to blue before you can react - but this method will work if you are carefull - pactice on a piece of unmachined unhardened stock to get a feel for how much heat to apply and for how long.

Ken

 

[coopertje]

Thanks for your answer Ken, I was completely wrong in my understanding :-[ You polish one side to just see better the color change creap up from bottom of tool to the cutting tip when tempering the broach! I though we where talking about finishing the cutting edges after grinding and tempering.

If nothing comes inbetween I will make another broach tonight. Since my grinding machine is not operational yet I will take a different approach. I will set my milling table to 1.25 degrees and mill the relieve in the broach, harden and temper it and then hone the front side of the broach with a stone.

Regards Jeroen

 

[coopertje]

Made a little progress this night. Started with modifying a indexer I bought last year. Its very reasonable build and very cheap, 45 euros. I did not want to change the table of the mill to 1.25 degrees since it is set to zero quite accurate. I had the idea to add 2 M5 screws at the front of the indexer to set the angle in a more accurate way and could leave my mill table at 0 degrees. Dis-assembles the indexer and cleaned the typical smelling chinese grease. Put it in the mill, drilled and tapped the 2 M5 holes. As you can see in the pictures the sides of the base look like a banana, not so good for clamping it in a machine vise.

Flipped the part in the vise and made the sides of the base straight

Assembled it and before mounting a collet checked the run-out in the spindle, it was a little over 0.01mm which is better then expected and very acceptable for making a broach.

Spend quite some time in setting the angle accurately, I calculated 0.253mm movement in height when moving the dial indicator 10mm over the blank of the broach. When found locked the vise and mounted a mill with a chamber on the cutting edges and start cutting. I am quite happy with the result, no need to grind it when making it this way.

Its not hardened yet, I will do that tomorrow.

Regards Jeroen

 

[steamer]

Looking Good Jeroen!

Watching intently! I intend to either A, Mod my indexer like yours, or B, mount my indexer on a sine plate in the vice.
Considering I have the sine plate....I'll probably do that.

Dave

 

[coopertje]

Thanks Dave! For sure, if I had a sine plate available I would go for option B too. I probalby will drill 2 extra holes on the back too, yesterday I had to fill out the back to have the indexted tilted forward (collet side needed to be lower then the backside)....

Regards Jeroen