Building KEN I Rotary broaching tool

[coopertje]

We are getting somewhere! Remade the broach yesterday and followed the advice given in hardening. It seems to work, made 2 hex holes, one in aluminum and one in brass. Not a single sign of use on the broach and it went in like cutting butter (could rotate the tailstock with one hand easily), thanks for the help!

If you look closely to the aluminum bar you will see that the hole was oversized, the broach cutted at the darker parts at the side inside the hole.

Procedure followed to make the broach:

1) mill the hex to size at 1.25 degrees angle
2) Wrap a piece of wire around the broach and heat it until carrot orange. Put it in cold water and keep moving until it cooled down
3) Clean up the shaft with sanding paper and the tip or with sanding paper over a file or a honing stone. Be careful to not damage the sides, just make them clean.
4) Heated from the back of broach and watch the straw color go up until the tip (this is not so easy to see) and again put it in cold water and keep moving until it cooled down. Now its tempered.
5) Clean up again the shaft with sanding paper and I honed the front side of the tip and the 6 cutting edges slightly with a fine honing stone.

Tomorrow I will make some different size of broaches. What would be the correct tolerance on broach cutting sides?

For example a 6mm hex broach, should it be spot on 6.00mm or make it slightly oversize like 6.01mm?

Regards Jeroen

 

[steamer]

Glad it worked out Jeroen!

I think .01mm clearance is fine for socket, but I wouldn't go any more than that...

Dave

 

[mu38&Bg#]

Very good. I will need one of these for sure. Especially seeing you don't need any special grinder to make the broach.

Machinery's Handbook says the ANSI/ASME spec for a 6mm hex socket is 6.02-6.095. I found this online. http://www.greensladeandcompany.com/pdf/Inspection-Hex Recesses.pdf

Greg

 

[steamer]

Thanks Greg! I stand corrected! :bow:

Dave

 

[coopertje]

Thanks Dave and Greg, that very useful information! I have printed the ISO table, now lets go to the shop to make some broaches!

Have fun, regards Jeroen

 

[Ken I]

Well done Jeroen - a couple more pointers.

When tempering cool down in liquid soap as suggested by Steamer) or oil - just slightly less of a thermal shock.

The chamfer needs to be at least as big as the corner to corner distance of the broach.
Imagine you had no chamfer and your toolholder is a bit worn and droops - it will snag the face off centre and be whirled around in an orbit until the cutting forces (tend to) centralise it. This imposes uneccessary stress on the broach and can snap it. (with a brand new holder like yours its not really a problem.)

If you want a sharp corner then make allowances to face off the chamfer later.

Ken

 

[coopertje]

Ken, I am sorry but I do not understand what you mean. If we call the grinded end of broach the tip length, do you mean that the tip length should be at least the corner to corner distance of the broach? In other words, don't make the tip length too short?

I have made my broaches before reading your comments, lets see what you think of them, I am open for any comment!

Measured my allen keys and they are all or spot on or below the mentioned key number. So I felt that I will have a lot of play when making the broach too big. My goal when making them was to be on the lower limit of the Iso Norm, 0.02mm oversized. I ended up with broaches that are between 0.015 and 0.03mm oversized which should be quite acceptable.

When the milling was complete I took the broaches to the lathe and made a small chamfer

For the smaller sized I prepared the blanks in the lathe so less material needed to be milled away

Here is my set after milling and before hardening. The dimensions (without tolerance) are 8, 6, 5, 4, 3, 2.5, 2 and 1.5mm (The 1.5 version looks really fragile, seems that it will snap off on the first use, did not try it yet….)

Then I harden them all and try to temper them accurately. Its quite difficult to see the straw color, one need some practice in this. I believe with most of them it went ok (second from left a bit too warm and 4th from left a little too cold)

Cleaned the sides with a honing stone and to hone the tip I put the broach in a collet such that the tip came out the back of the collet (to not damage the front of the collet). The collet is used as a guide to keep the tip straight on the hone.

Made a nice storage box (old Clarkson collet holder box) for the tool including the broaches. There is also room for the spare bearings and the prepared drills with asymmetrical tips (maybe new chinese drills have this feature as standard?).

It has been proven that you can make the broaches without a grinding machine. However next time I will make them on the tool grinder (hope the weather becomes better soon, want to finish it!). It much quicker in setting up the angles and also the cutting sides will be better finished (sharper) then when made on the mill. Especially the small broaches are a pain to hone with a stone!

I got an offer from Peter from polygon solutions. He offered me to send me a professionally made broach for me to try in my holder. I have discussed this with the moderator, after all this is a place to share our hobby! I am very pleased that they agree with it, I am eager to test the difference between a professional broach and a shop made version. I will try to make a test with a 6mm hex broach, 1 made on the mill as I did today, one made on the tool grinder and one supplied professionally. It will take some time, but when I have the results I will post them here.

Regards Jeroen

 

[mu38&Bg#]

How do these wear Ken? By making broaches something larger than the minimum, would it allow for sharpening of the cutting face of the broach before scrapping the tool?

 

[Ken I]

Jeroen, you broaches are just great. That's a really lovely set you've made yourself there. You might reduce the length to width aspect on some of the smaller broaches on future replacements.

My comments were related to the drilled & chamfered hole in the material being broached - that is the hole you must predrill must be a bit bigger that the across flats distance and the chamfer must be a bit bigger than the across corners distance.

Dieselpilot - at one stage I used to have the broaches made top limit specifically for regrinding - in practice the edges tend to crumble and were not worth regrinding - remember this was in a production environment so no one noticed the broach was dull until it was buggered - for home use regrinds would be practical - removing as little material as neccessary - if the edges appear to be bit dull.
Hard material like HSS tends to chip away at 45°, material like hardened drill rod tend to go dull and generate "lands" on the clearance - like Jeroens earlier pictures of an insufficiently hard broach.

Sorry - kind of a yes, no, maybe sort of answer.

A professionally made HSS broach will require a little less force, last much longer and the hole will most likely be better (more a function of your accuracy & finish than anything else) but for hobby use that's not the point of the excercise.
Like many cutting tools they are cheaper bought than made yourself - but again doesn't provide the sense of acomplishment that doing it yourself does.

Ken

 

[ref1ection]

This has been an interesting and very informative project to watch.

Ray

 

[mu38&Bg#]

Jeroen, a box and spares! Excellent.

Ken, that makes sense. I'll probably buy the broaches once the time comes. There is a small volume product I'm thinking of making.

 

[Ken I]

Jeroen,
I trust you are going to post your finished box-set and a video of it working under finished projects ?

Ken

 

[coopertje]

Thanks for the comments and interest Ken, Greg and Ray! You sure know what you are talking about Ken! Glad that my broaches look ok, and the chamfer on the prep-holes is received loud and clear this time.

When the box is finished I will show it here. Also will try to make a video (don't have to big expectations, my video making capabilities are even worse the my machining ones). Probably it will take a week or 2, I am leaving tomorrow afternoon for work abroad. If I remember I will also try the broach in the mill, then its better to see the action.

CU, Regards Jeroen

 

[coopertje]

Took a little bit more then 2 weeks, is quite busy at work and the RC helicopter season has started again.

Yesterday I made a storage for the QC tool holders. I collected quite a bit (18 in total) over the years and still I am changing tools in the holders. I believe you will never have enough of these….

As promised below some pictures of the finished box. As you can see needed to make some space in the cover to have the broach holder fitted.

I have tried to make a movie of the tool in work in the lathe as well as in the mill. If you look closely to the broaching in the mill, the tool rotates a little at the beginning. I think I need to give it more pressure from the start, even though the fit of the Allan key is the way I like it, nice and tight.

[ame]http://www.youtube.com/watch?v=sso8Jpf4s30[/ame]

Got the broach from Polygon Solutions. Must admit that the finishing and quality is top level! Below the professional broach on the left and the home made on the right (as if the difference would not be obvious…). Note the hole in the Polygon broach, in this way the air can escape when mounting the tool in the holder but also during the broaching process. Since my prep holes are quite oversized I do not miss the hole in my home made broach.

Made an adapter for the Polygon broach, this has an 8mm shaft were I need a 10mm one

I have tried both broached in the lathe in Aluminum. To my surprise I could not detect any noticeable differences between both broaching bits. The force to cut is similar and also the finishing of the hole is the same. Maybe in steel there is a noticeable difference, or it might be the life time of the tool. Since I will only make a few hole per year it will take me a long time to find the answer….. I am sorry Peter, I will not become a customer, but thank you again to give me the opportunity to test the differences :bow:

Its hard to photograph, here is the best I could do for the polygon broached hole

and the home made broached hole

I am happy that I made this tool, I can only encourage others to do the same!

Have fun, regards Jeroen

 

[vcutajar]

Jeroen

A fine bit of kit you have made for yourself. :bow: It will last you a lifetime.

Vince

 

[Ken I]

Well done Jeroen - nice to see someone actually build and use it - thanks for the vid.

When using it in a mill you can see how it got the name "wobbly broach".

Regards,
Ken

 

[coopertje]

Thank you for your comment Vince! Ken, special thanks to you for making this tread possible, I really enjoy the tool :bow:

Regards Jeroen

 

[steamer]

Nice Job Jeroen!

gotta build me one of those!

Dave

 

[Lesmo]

Nice one Jeroen

Safely tucked away for the future.

Les

PS Your video making skills are much better than you said they were.

 

[coopertje]

Thanks Les! Using Imovie makes live a little more easy.

Regards Jeroen