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Peter.
03-01-2009, 05:33 AM
What's the most common angle for dovetails as used on metalworking equipment? Is it 45 or 60 degrees? Why would one chose a particular angle over the other if making a tool or attachment?

John Stevenson
03-01-2009, 07:49 AM
Depends on what cutter the manufacturer has in stock :rolleyes:
60 is normal but I have come across special like 65 where the manufacturer wants to keep the after market parts.

The Germans are handy at this :rolleyes:

Also saw some early Taiwanese mortisers with 65 on the body and 60 on the slide. :eek:

Terrific bodge but I modified the slides [ body to big to do anything with ] by putting a cup grinding wheel in the mill drill, dressing the side to 65 with a Black and Decker valve refacing jig and grinding along the sides to clean up.
Them made a wider gib strip, the fact it was offset slightly didn't matter as the bottom vise was adjustable.

I was expecting a rough job but enough to get the guy out of trouble, in fact I got a superb finish, better then the original milled finish.

.

Jpfalt
03-01-2009, 09:52 PM
The angle of the cut depends on the direction of loading on the dovetail. If the loading is pressing the dovetail into the slot then the angle will most likely be 60 degrees or steeper. If the loading is pulling the dovetail out of the slot, the angle will be 45 degrees or shallower.

The main reason is that steep tapers tend to be self locking under pressure. Also, a 45 degree dovetail with .001" clearance will allow .0014" of lift while a 60 degree angle with .001" clearance will allow .002" of lift. Under a lifting load, the 60 degree dovetail will require approximately 30% more force to slide the dovetailed part.

For lateral loading only, the 60 degree dovetail will have less lateral slop and require less force to slide in operation.

Your Old Dog
03-02-2009, 08:16 AM
Jpfalt, thanks for the great explanation.

I have both, bought the 45 degree set first and thought they looked too fragile for my experiance level on the mill. I bought the 60 degree set and they look like they will take more punishment to me as the point they come to is more obtuse.

Forrest Addy
03-02-2009, 09:41 AM
MY Rockford planer has 50 degree dovetails. They cam be all over the map at least theoretically but I can't recall ever seeing a 45 or 60 degree dovetail on any production machine. On;y one-off where a dovetail cuttier was handy.

Needless to say, set the angle and verify via dial indicator before you re-cut a dovetail. There's enough dovetails cut to carefully match the fitter member but maybe a degree or so off the nominal angle to put a monkey wrencj in an otherwise smoothy flowing work sequence.

malbenbut
03-02-2009, 10:56 AM
55 degree dovetails are quite popular on many British made machine tools.
MBB

TGTool
03-02-2009, 01:18 PM
55 degree dovetails are quite popular on many British made machine tools.
MBB

Would those be Whitworth dovetails then? Rounded corners too? :)

malbenbut
03-02-2009, 02:07 PM
Quote
Would those be Whitworth dovetails then? Rounded corners too?

Nope straight forward dovetails.
Nearly all dovetail arbor supports on older Brit machines are 55 degrees.
Dont know about American tools. Maybe someone could measure dovetails guides on some older USA iron.
MBB

Steve Steven
03-02-2009, 05:02 PM
The ram on my Van Norman 12 has 55* dovetails.
Steve

malbenbut
03-03-2009, 10:00 AM
Quote
The ram on my Van Norman 12 has 55* dovetails.
Steve]
It seems some Britt and American machines have 55 degrees in common.
Any particular reason for 55*? its much easier to buy 60* dovetail cutters
MBB

Jpfalt
03-03-2009, 11:36 AM
Some people obsess about things. 55 degrees vs 60 is pretty much an arbitrary pick, but somewhere there is someone who will insist it must be 55 degrees or nothing.

I've seen fistfights between saw filers over the question of whther the bandwheel should be flat or crowned.

rohart
03-03-2009, 11:27 PM
I'm pretty sure my Lorch uses 50 degree dovetails, and they need tidying up. I'm intending to use a 45 degree cutter with the work mounted at 5 degrees up from horizontal.

For all I've read about scraping, I'm not clear about whether scraping dovetail surfaces is on the cards.

Astronowanabe
03-04-2009, 03:54 AM
Quote
The ram on my Van Norman 12 has 55* dovetails.
Steve]
It seems some Britt and American machines have 55 degrees in common.
Any particular reason for 55*? its much easier to buy 60* dovetail cutters
MBB

as far as I can recall, 55 deg is about the steepest a pile can get
before the sides start slipping/blowing out
eggheads of old probably figured out some way to apply that to threads and dovetails