Compact rotary broach

[Arbutus]

The hunnydo list was completed about a month ago and my love gave me a pile of round tuits to use.

The first one was used to complete (and document) this compact rotary broach. My design is similar to the Hemmingway kit, although I have chosen different bearings and different dimensions to suit the stock I had on hand. It should take about a half day to make. The cutters are also easy to make from O1 or A2 tool steel. If you don't make your own tooling, then this design accepts any standard commercial 8mm shank x 28mm broach. Longer broaches can be fitted, and the head can be adjusted to allow for the extra length.

There are PDF drawings, one for each part, together with some exploded views.

 

[Arbutus]

PDF drawings...

 

[YYCHM]

How many PDF drawings should there be? You posted two of the "shaft Drawing"?

 

[Arbutus]

How many PDF drawings should there be? You posted two of the "shaft Drawing"?

should be correct now.

 

[jcdammeyer]

The hunnydo list was completed about a month ago and my love gave me a pile of round tuits to use.

The first one was used to complete (and document) this compact rotary broach. My design is similar to the Hemmingway kit, although I have chosen different bearings and different dimensions to suit the stock I had on hand. It should take about a half day to make. The cutters are also easy to make from O1 or A2 tool steel. If you don't make your own tooling, then this design accepts any standard commercial 8mm shank x 28mm broach. Longer broaches can be fitted, and the head can be adjusted to allow for the extra length.

There are PDF drawings, one for each part, together with some exploded views.

View attachment 36188View attachment 36189View attachment 36190View attachment 36191

Wow! Impressive work. Something for all of us to aspire to.

 

[Sailor]

Thanks for the drawings, nice work.

 

[Mcgyver]

Well done and good of you to share the drawings.

 

[140mower]

I have gathered all the bearings and metal bits to make one of these as well. Unfortunately when I went to make mine, my bucket of time had spring a leak and was empty.....

 

[Tom O]

I have a question about the offset holes seen below the center line as there doesn’t seem to be any dimension. I take it it is for dialing in the size/fit so I would think it‘s not critical.

 

[Arbutus]

I have a question about the offset holes seen below the center line as there doesn’t seem to be any dimension. I take it it is for dialing in the size/fit so I would think it‘s not critical.

View attachment 36304

View attachment 36305

Not critical - M4 screws and a 4mmx4mm slot are shown. On the prototype I actually ended up with M6 screws. The offset is 1mm, which places the centre of the cutter on the axial centerline. Longer tools will require the head to be lowered slightly. I allowed 4mm of travel but 2mm would be plenty.

 

[Arbutus]

FWIW, the O1 cutters work great in anything other than tough steel. The A2 cutters are, in my opinion, easier to make and cut 1045 and stainless etc beautifully.

The starting hole dimension for Hex holes should be the same dia as the across-flats dimension shown on the cutter drawing. The hole MUST be chamfered to start the cutter properly - around 1mm is enough. For square holes, the starting hole should be a little larger (3-5 thou) than the AF dimension, because this very significantly reduces the cutting pressure that is needed (less area being sheared per rev.).

Don