Group Project: Rotary Broach-- Building complete, all shipped out!

I see you are crunching numbers on shortening the OAL. I was considering allowing some extra thickness on the backing plate so no matter if the arbor is .625 or .750 long (threaded shank), it could be tightened down with no worry of bottoming out. Also, I now the off center is taking up it's part of the pre planning, what if the backing plate had a boss and the spindle body was recessed and you could have 4 sets screws around the outside for centering?
I.E. below. The boss could still be ground with the 1* of angle

adj.jpg
 
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GunsOfNavarone said:
I see you are crunching numbers on shortening the OAL. I was considering allowing some extra thickness on the backing plate so no matter if the arbor is .625 or .750 long (threaded shank), it could be tightened down with no worry of bottoming out. Also, I now the off center is taking up it's part of the pre planning, what if the backing plate had a boss and the spindle body was recessed and you could have 4 sets screws around the outside for centering?
I.E. below. The boss could still be ground with the 1* of angle

View attachment 369084
Click to expand...
Something like that recess was one of my thoughts on that. But the more I see it, I wonder how much this would be something we do!

I have a boss built into the backing plate for the arbor, but note the backing plate thickness doesn't matter for the offset. The important "length" is front of backing plate to tip of bit. So any additional thickness to the backing plate is fine.
 
So this offset thing is new to me in regard to the rotary broach. Those of you that have more understanding of it, chime in. I just want to make sure all challenges are addressed so we don't have one of those, "I wish we would have done..."
A thicker back plate would allow a hole of varying depth for different arbors.
 
GunsOfNavarone said:
So this offset thing is new to me in regard to the rotary broach. Those of you that have more understanding of it, chime in. I just want to make sure all challenges are addressed so we don't have one of those, "I wish we would have done..."
A thicker back plate would allow a hole of varying depth for different arbors.
Click to expand...
I've already got the 'bore' area for the arbor at ~.750 (with some room to go deeper). Presumably a washer could be used to make it longer if necessary.

Currently I'm wrestling with FreeCad's TechDraw to try to make 2d drawings that aren't terrible looking. I think I made a mistake trying to do the backing plate first :) The 1 degree angle confuses the heck out of the drawing panel in a number of different ways!

The way it lists tolerances are a little strange too, so I'm still working through that too. That said, I think I am doing a good job identifying the 'important' dimensions, with most of my dimensions as "unimportant". For example, on the backing plate, the 1 degree angle is critical, as are the bolt-hole spacing, otherwise we're looking at mostly 'fractional-ish' dimensions. I still can't figure out how to show fractional dimensions either though :)
 
alright, drawings "done" ish.

Please review these images and let me know if they have enough information. THis is still my first try at CAD, so i could still have messed stuff up.
 

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  • Main Body.png
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While your drawings are like mine, not professional, they show what is needed.

Got my Spindle drawing, are we going to leave them round (1.50) or.... what.? I see the spindle dwg doesn't show the through holes/slots.
 
T Bredehoft said:
While your drawings are like mine, not professional, they show what is needed.

Got my Spindle drawing, are we going to leave them round (1.50) or.... what.? I see the spindle dwg doesn't show the through holes/slots.
Click to expand...
Yep, the spindle is round (1.5" OD at the largest spot).

There are only two inner bores plus a set-screw, which are on the right image, though the renderer apparently made them look a lot like the 'measurement' lines.

In the 'face' side, there is a .500 +.010/-0 diameter bore, .750 deep, with a square bottom. In addition, there is a .125 (or so, the diameter doesn't really matter since this an 'air relief' hole) bore all the way through (#3 in the drawing).
 
And what keeps it from revolving independent of the Main Body?
 
T Bredehoft said:
And what keeps it from revolving independent of the Main Body?
Click to expand...
Nothing, the intent is to have the spindle revolve independently of the main-body. It is on 2 bearings intended to let that happen.
 
In my mind, the way a rotary broach engages a hole is kind of like a U joint on a car. The axes of rotation are angled with respect to each other but the axes intersect at a point that is the tip of the cutter.
Robert
 
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