I made a thing...

[shipto]

...to grind broaching bits on my surface grinder. Pic 1 is the jig in place on the grinder, I can set the angle needed and lock it in place then use the protractor to set the facet to be cut. It is locked in position by way of a bar going under the collet with a dimple and ball bearing to wedge it solid.
Pic2 is the result of my test to make a 8mm hex broach out of a M14 tap shaft.
Pic3 I pushed the broach through a scrap bit of aluminium and the allen key fits perfectly.

[AdeV]

Oh, that is NICE!

I cheat when making hex holes - I use a EDM machine Although that only works if the thing I'm "drilling" is quite small, otherwise it won't fit in the tank 

[Muzzerboy]

Doesn't look as if you are using this as a rotary broach as such, so presumably you drill a hole and simply press the bit through it? Or is there also a rotary broach chuck(?) associated with it for use in your pillar drill or milling machine?

[shipto]

Doesn't look as if you are using this as a rotary broach as such, so presumably you drill a hole and simply press the bit through it? Or is there also a rotary broach chuck(?) associated with it for use in your pillar drill or milling machine?

It will be used as a rotary broach I just havent made the chuck yet. I just pressed this through the aluminium because I wanted to see the fit but yes it was a drilled hole 8mm then slightly countersunk to centre the broach and pressed through.

[Muzzerboy]

Nice looking part. This is one of those tools I fancy having a go at. I'd want it to be usable in both the lathe and milling machine. I'll be interested to see how you get on.

I don't know if you noticed, but RotarySMP has been gaining some experience(!) in making these bits recently. He has a chuck sent to him by one of his viewers.
https://www.youtube.com/watch?v=HZHeBOYlOjQ

The chucks look reasonably easy to make once you've figured out the best way to hold the body at the required 1 degree angle. Famous last words!

[shipto]

Nice looking part. This is one of those tools I fancy having a go at. I'd want it to be usable in both the lathe and milling machine. I'll be interested to see how you get on.

I don't know if you noticed, but RotarySMP has been gaining some experience(!) in making these bits recently. He has a chuck sent to him by one of his viewers.
https://www.youtube.com/watch?v=HZHeBOYlOjQ

The chucks look reasonably easy to make once you've figured out the best way to hold the body at the required 1 degree angle. Famous last words!

Thank you for the video, I have subscribed.
As for the chuck I am still mulling it over but have collected a few parts and started drawing my ideas up on freecad. My design will hopefully be usable in my turret head so I can mount drill, countersink and broaching tool for quicker operations. I will set up a thread on "projects" when I start.

[shipto]

Oh, that is NICE!

I cheat when making hex holes - I use a EDM machine Although that only works if the thing I'm "drilling" is quite small, otherwise it won't fit in the tank 

I looked into cheap and cheerful EDM when I first looked at doing this but decided that for the quantity I hope to be needing it would take too long. Having said that I would really like to play about with EDM but must not get distracted. 

[shipto]

When I went to the midland model engineering exhibition last week I picked up some 1/2" round hss which are about 65mm long so cut in half can make two bits each.
Spent most of the weekend messing about making the bits, so far I have made a 10mm and a 6mm there is a 8mm still in the jig but I messed up it up so its undersize but no big loss I will just grind it down to make a 5mm broach.
The 6mm seems to have come out really well and the 10mm is measuring good too.

[philf]

I've just made the rotary broach with its one degree offset but not yet a broaching tool to try it out.

Mine takes 12mm and 6mm dia tools (6mm with an adaptor).

I already had a suitable INA combined needle and thrust bearing so designed it around it. It has a 2MT arbor so it can be used in the bench drill or lathe tailstock (with a 2MT to 3MT adaptor)

[shipto]

An adapter is a good idea actually, would certainly save time grinding the smaller ones. I do have the beginnings of the tool holder but I am making mine with adjustment to dial it in. I will post it up when done.

[philf]

I just made a 10mm hex broach (out of silver steel). I've only tried it in brass so far and it needs a lot of force to broach the hole pushing the bar back through the chuck unless it's very tight.

I'll try a 6mm hex next and then, if it works OK in brass, maybe try it in steel.

[shipto]

I just made a 10mm hex broach (out of silver steel). I've only tried it in brass so far and it needs a lot of force to broach the hole pushing the bar back through the chuck unless it's very tight.

I'll try a 6mm hex next and then, if it works OK in brass, maybe try it in steel.

The force required is one of my main worries especially as I have done things the wrong way around strictly speaking as my parts are already threaded. I will make a split nut or something to hold the parts in with matching threads so if it moves in the chuck it wont mash them up.
just completed the 8mm broach and I am really pleased with how my little grinder is performing, its really good when I dress the wheel before starting and I have included pics of that and the start of the tool inself.

[philf]

The force required is one of my main worries especially as I have done things the wrong way around strictly speaking as my parts are already threaded. I will make a split nut or something to hold the parts in with matching threads so if it moves in the chuck it wont mash them up.
just completed the 8mm broach and I am really pleased with how my little grinder is performing, its really good when I dress the wheel before starting and I have included pics of that and the start of the tool inself.

If you're putting a hex socket in a screw the head should limit how far it can move in the chuck.

I have split sleeves for lots of thread sizes - very useful. A sleeve with a collar on one end would stop the sleeve pushing through the chuck. I'll make some!

[philf]

I made a 4 and a 5mm hex broach this morning.

I used silver steel and tried them putting a hex socket in mild steel. The 4mm worked ok with a 4.2 pilot hole but when I tried a 4mm hole it took the corners off the broach. The 5mm was no better  - even with a >5mm pilot. 

I hardened the broaches in oil. I'll try water next to see if they do a better job.

Only takes a few minutes on the mill with my dividing head set pointing 2 degrees down. I put the cutting angle in the end on the lathe at about 8 degrees.

So far a lot of effort with little to show for it.

They work OK in brass but I've not come across many socket head screws in brass!

If the next, water hardened, broaches fail I'll try HSS - probably by silver soldering broken end mills into a 12mm shank.

[shipto]

RDG are selling 5 x 12mm x 100mm tool steel for just under £16 I assume theres some postage to pay too.

[philf]

Thanks Shipto,

12mm HSS would be a last resort. It would take me ages to grind it to a small size. When I get a few minutes I'll try a water hardened one and, if that doesn't work, go for 6mm HSS which RDG do 5 pieces of 100mm long for £9.95 with free postage.

Phil.

[Muzzerboy]

I hardened the broaches in oil. I'll try water next to see if they do a better job.

Did you temper them after hardening? Failure to do so would leave them very brittle. Typically, that would result in the sharp corners breaking off.

[John Rudd]

Use a code 12769, to get a discount…(5%)… but no RDG prices inc post.

[philf]

I hardened the broaches in oil. I'll try water next to see if they do a better job.

Did you temper them after hardening? Failure to do so would leave them very brittle. Typically, that would result in the sharp corners breaking off.

I did - the corners didn't look as though they'd broken off - more like worn away.

I have some KE672 which I've made cutters out of which have been capable of cutting clock pinions in silver steel. I'll try one in that.

[philf]

Use a code 12769, to get a discount…(5%)… but no RDG prices inc post.

From the RDG website:

FREE UK Delivery
For all orders going to anywhere in the United Kingdom, the free postal details are below.
Orders up to £30 2nd class post 2-10 working day service.
Orders from £30-£100 will be shipped by Royal Mail tracked 48 a 2-10 working day tracked service.
Orders £100 or above or over 2 kilos will be shipped Fedex for next working day for mainland UK and 2-3 day shipping for Scottish Highlands, Islands, Northern Ireland, Isle of Man, Isle of Wight.

Phil.

[John Rudd]

Mebbe I mis wrote it….

I meant their charges inc postage.

But for a discount of 5% use code 12769…..when checking out.

[philf]

Mebbe I mis wrote it….

I meant their charges inc postage.

But for a discount of 5% use code 12769…..when checking out.

Thanks John - I'll try it - Phil

[shipto]

First attempt at a holder did not work well, it was fine pushing it into the part allbeit a little more effort than I had expected which could have been because it wasn't quite centred properly. however when trying to withdraw the broach the whole thing came apart.
So I altered the design a little to ensure that it is running on a trapped bearing while it is being withdrawn. If it works ok this time I wil post a drawing.

[shipto]

And worked out a professional tool to sharpen tips.

[shipto]

Cant say fairer than that! 

[philf]

What size pilot did you use?

I haven't got round to making a HSS broach for mine yet after my silver steel failures.

[BillTodd]

Looking good.
What's the pressure like now you have sharpened the tool?

[shipto]

What size pilot did you use?

I haven't got round to making a HSS broach for mine yet after my silver steel failures. Lol lol

6mm for a 6mm hex.

Looking good.
What's the pressure like now you have sharpened the tool?

The pressure needed at the beginning is very good but adds up as it cuts but I think if I remove that with the drill then take another bite I can get the hex a bit deeper. I will try that tomorrow.

[shipto]

I set it all up and I am quite pleased with the results. however I discovered that the selection of 6mm allen keys I have vary from 5.97mm (the one I measured to get the size of the broach) to 6.05mm which will fit but gets a bit stuck as I made the broach 6.05mm so I might need to make another nearer to 6.1mm.

I have included pics of the setup and end result but my phone is struggling to get a decent close up of the hex itself.

One thing to note is to do with setting the tool, I found it much easier to set when I drilled a slightly oversize hole (6.5mm) in a plate and put it in the mill then turned it by hand and set it until the plate did not move when turning the broach tool rather than trying to clock it up on the lathe.

[RotarySMP]

I found the system extremely sensitive to clearance diameter. Learned the hard way with too small holes