I posted this write up a long time ago(in two parts..both here), and it is long, but it explains the steps necessary to do the job .
I have made many holders for special use like:
1.bored on ends for boring bars (1/4,3/8,1/2)
2.ball turning tool.
3.boxtool
4.indicator holder etc.
but here is my procedure....
I have measured both AXA and BXA toolholders from Aloris and will use that information here.
First, the proper way to measure a dovetail (DT) is with dowel pins a bit smaller than the DT height/depth.
Normally the pins are layed in the DT and an adjustable parallel is expanded between the pins , and the parallel is then measured with a micrometer . This gives a very accurate dimension.
The gauge I made was a way of shortcutting this process, but lets follow through the long way first.
Put the long bar (1.25 X 3X 12"+)in the mill vise and cut a slot for AXA 1.328 wide by .380 deep (1.375 by .418 for BXA) by the length , in the center of the 3" width.
Cut your 60 degree DT on both sides ,( Roughing cut!) and lay the pins in the groove. measure between them with an an adjustable parrallel or if not available, a vernier caliper. Keep in mind , that the DT cut must be high enough on the wall of the slot so that the .25 pin hits the DT just above its center and is tangent to the DT
The target dimension is 1.006 between .25 pins for AXA and 1.085 for BXA
IF YOU GO PAST THIS,THE PART IS SCRAPPED !
now if you hit it , HOTDOG!, the pins should also be .128 (.166 BXA) from the flat face, which is the top surface as you mill. This you measure down to the pin with a depth gauge, or vernier caliper.
So now the part can be flipped over and the tool slots cut and then the bar is sawed into pieces.
But wait , the hard part is hitting the DT and pin dimensions dead on and risking scrap.Also your DT cutter should never drag on the bottom as it dulls the cutter quickly, and lastly, the IMPORTANT dimension is the relationship of the DT to the flat mounting surface.
So to use this to our advantage, if we make the DT a little deeper (not wider), we have the advantage of hitting the width , then removing the flat surface until it matches the requirement.
This means that you should mill the slot depth about .010 deeper and also take out another .005 in depth for about an inch wide in the middle so the DT cutter won't cut there.(WARNING Don't make the .005 deeper for the full 1.3xx slot width, as it will screw up your pin measurement !!!!)
now by starting the DT cutter .010 deeper, if you overshoot the DT pin width, it's not a problem.
shim the pins on the bottom (say .005) and measure again....if OK, then shoot for the .128 to the flat by milling the flat till it is .128. BINGO, even thought the pins are wider then wanted the part will work perfectly because the RELATIONSHIP TO THE FACE (.128) was held.
Now since I don't worry about the exact pin spacing results, I made a gauge that has the pin mounted and spaced already and also the .128 dimension to the edge, so when I can stick it into the end of the DT on the bar, it shows me how much to remove from the top flat surface to make a good part.
This gauge also serves to locate the tap hole locations for the toolholder and I don't have to layout each one. Just dropp it on the toolholder and drill in the drill press.
Now here is the original post:
I recently wrote up my procedure for a friend, so I am reprinting it here, since you and maybe others want to make some holders. The following is for the 100 "A" series, so yours should be appropriately larger. Normally, when dovetails are machined, you measure between them with parallel gauges to get the proper dimension. there is a shortcut though as follows:
No it isn't necessary to grind the holders. You can if you wish, but it does
not change performance, neither does the type of steel, unless you expect to use it
over 10,000 times. Hardening is also unnecessary, BUT parallelism of dovetails IS most
important !
To start my discussion, take a existing Aloris tool holder and put it down
on the table with the tool holder part facing you and the dovetail on the
farside. have the set screws and height adjustment screw removed for our
discussion. The surface on the far side is what I call the "flats" as it
goes against the tool post.
Well , I believe one of the secrets( if you can call it that) is to make a
gauge from a piece of C.R. or OI 1/4 X 1 x 3 approximately and if it has a
lip, even better.
So this gauge will sit on top of the toolholder and the lip should hook the
far side. The cross-section would be L shaped, but laying down on top of the holder. Now if you
can, pick it up and the holder and flip over (clamped would help) and drill two holes
(.2500) against the dovetails for dowel pins- using the dovetails themselves
as drill guides-you get a doweled jig/gauge that measures the dovetail
spacing and its distance from the "flats".
This is important since the depth of the dovetail means NOTHING.
What's important is the spacing relative to the back (flat ) mounting
surface, and dowels are the best way of measuring a dovetail and the lip, is the distance. I then press
in 2 dowels about 1/2" long
Once the gage is made, I take a bar of 1018 C.R.Steel - 1 1/4 (1" min) X 3" X
15" or so to make about 9 holders.
Cut down the center of the bar with a mill equal in width to the dovetail opening
(smaller dim)or a little larger (doesn't hurt, cause you don't want a sharp
dovetail edge).
This would be about (From Memory Now ! may not be exact) 1 1/4 wide by 3/8
deep by length
The cut must be deep enough so the dovetail cutter doesn't" hit the bottom"
same as doing a "T" slot. Take a cut with your 60 Degree dovetail cutter.You should go slightly deeper then a commercial holder.
Now I lay the gauge on the end of the part and
hook the lip on the top surface which is the flat, and see if the dowels fit
in the dovetail.Careful, if the lip is loose, you have scraped the job!
THERE are 2 ways to go here.
1>If I want to grind the flats, stop when
the pins fit , but the lip is lower then the flats ( means I can't hook it)
If the hook is .002 to .010 short, it means I can set it up on a surface
grinder and grind down the flats till the gauge slips in.This is what I
usually do.
2> If you don't grind, Flycut or face mill the "flats" till the gauge
fits....LIGHT CUTS,cause the gauge if loose, means that the holders will be
sloppy.( One of the reasons that the tool post handle is not at 4 O Clock as it
should be when clamped
Once the "bar has the right dovetails, I flip it over and layout the 1/2 X
1/2 tool slots using a holder as a guide, and machine them a right angle to
the bar...fast this way...then saw cut them out.
Then I clamp my Aloris Tool Post "t" nut in the milling vice, and mount my
tool post to it,making sure it is plumb. Now put the holders in the post
where wanted and mill the tops, and flip and do the bottoms.OR you could put
a piece of 1/2 X 1 into the slot and set it on the vice jaws and mill also
without the post.
That's it....except I didn't tell you about my gauge exactly.... it has the
dowel pins and I don't have a lip, but eyeball it, and I also have the layout for
all 4 clamp screw holes and the height screw hole. these are tap drill hole sizes
, so I can take a new holder and set the jig on top and drill the holes in
the drill press...the dowels hold it in place.
To finish, I belt sand them lightly to remove tool marks but watch...no
tapered grinds,break corners and then use Birchwood Casey Tool Black and
they look good.
In the past , I have made the Height screw knurled knobs etc. The last batch
got real Aloris adjusters....MSC sells them for about $5.50 nuts/screw/washer as a
kit and the are the nuts !
If you feel nervous about the Dovetails , just cut the end of the bar in about 1" and keep using the gauge till you get the right cross slide settings. Also try to cut one DT completly through and sneak up with the other side,so you don't have two variables.
One last thing, any left over piece from the bar is not tossed. I have a 3/4
inch high boring tool holder ...drilled for a 3/8 boring bar
And one a 1/2 high for a dial indicator mount...who says they have to have
open sides!
have fun and hope this helps