Diamond Grinder Part 3: Making a Keyway Broach 

I remember watching this video 4 years ago when it first came out - I can't believe there's only 23 (or 24 now) comments and 28k views. How far this channel has come in 4 years!

I am very impressed about the cleanlyness and organization of you workshop, and the way you do any task!

Thanks for this, James. The restoration project on which I volunteer (Battleship Texas) asked if I could cut keyways in some bronze gears for the ship's 5" guns. The originals had male keys as part of the original castings but after 110 years many had broken off. This tool solved the problem. The cutter on the one I made is 3/16" square so the dimensions are a little different but it's still your design. I didn't have any 4140 or tool steel on hand so it was made from 1/2" 12L14. It's adequately stiff to cut smoothly once I got the tool bit geometry worked out. I had a scrap of brass for testing. Too much angle caused it to dig into the workpiece. I ended grinding a small flat on the cutting surface with a 300 grit diamond stone for sharpening chisels. The cutting effort is very low.

This build had to help inspire you to get you manual mill !

Hey, as usual great content. Every morning now, I wake up early, fire-up the compressor (much to the delight of the neighbors) and try some new procedure on my new PM935 mill. Lots of failures, many successes and lots of learning and fun. Today's project was this Single-point Broach. Turned out great, but I prefer just using it on the PM935 than with the CNC Mini-Mill. Thanks again!

Thanks again man great vid quality [ production ] sound and cam angles. I luv ur OCD :-) Also like your detailed Fusion 360 commentary and vid. Ive grabbed a few cool new tactics for Fusion from you too. BTW - who the heck is downvoting your vids - its always 3 people - what the hell is wrong with people. No Adds - No Patreon requests - whatever people. Show some respect ! Thanks James!

Thank you so much for your video and sharing your expertise. I am interested in learning to be able to work like you. God bless

I have had success using a cutter like your first one, except for being shorter and making the end of cutting edge concave, usually a broken endmill is what I use. Like you said you needed the extra reach on this project n the new tool should work great.

Hi James. The original was just too thin. It's beam theory - double the depth and the bending is reduced by eight times (cube law). Carbide would help, it's stiffer, and a holder would reduce the overall cost - which is essentially what you did. Other channels have made things along your original lines work, but they were for manual use and the result could be 'fettled'. I can see that for CNC something more rigid would be better. BobUK.

I could smell the grinding as you shaped the cutting tool.

It would be a good project to add a UP/DOWN switch on the head of the mill to move the Z axis to help position it for tool changes and drilling without having to go back to the to controller. (Since you can already use the quill for drilling

Thanks for all your content! i have a G0759 (basicly the g0704 with a dro) and I converted it to cnc with Hoss's plans. I took the DRO off the mill and put it on the g0604 that i just got! We basicly have the same equipment so i can relate to your channel alot. Do you have any plans to make the power draw bar or motor upgrade. If you do could you provide a parts list maybe? If there is anything i could do to help out please contact me. Happy Thanksgiving to you and yours.

Looking thru your old vids, watched this. Nice tool ! A few questions; 1) Most broaching sets I've seen use a sleeve to push the cutter toward the intended slot. Would that have worked with your original long HSS cutter? 2) The slitting saw made an odd (cyclic) sound. Arbor out of round?

I’m thinking of building this. Drill rod is HSS right? Did you need to use carbide drills and slitting saw?

Nicely done, looks like it will work. I have one stupid question though - is it actually a broach when it has just one tooth? Linear broaching tools are distinguished by their multiple cutting points, so a lone single point bit doesn't seem to qualify. The interwebs are all over the place about what people call the process of cutting a keyway, regardless of the tool/machine being used. I'd be willing to bet there isn't a machine tool catalog where you can buy that bit under 'broach' anyway :)

Doesn’t HSS lose it’s hardness if you allow it to get red hot during grinding ?

Does someone sell parts like this? I saw CncBroachTools one, but they don't have a price on the website (meaning I can't afford it)

Good video. Happy Thanksgiving! Praise Jesus for all He has done for us.