How do you accurately measure the angle when you rotate the milling head?
Is there a relatively easy way to measure the angle? For example, if I want
to cut a 65 degree angle with an end mill I can put a straight rod extending
out of the spindle and use an adjustable protractor to set the angle of the
head but what other methods are there?
Put your protractor head on your machinist's ruler, and put the head
on the table. Set the angle to whatever you need. There is a machined
boss on the side of the BP head which you can set against the rule. If
you put a white card behind it and look closely you can match the angle
pretty well. That's as far as I've ever gone in precision. - GWE
It would depend on how accurate you want to get. Grants idea with the
angle head will probably give you +- half a degree, or .005/inch. I you
have a set of inspection angles, clamp them to an angle plate or in a
vice and run the indicator in the spindle, up and down the side, this
should get you within a couple of tenths over 2-3 inches.
If you have a sine bar, that will get you the closest.
It's a lot more complicated that it appears. Because Bridgeports have a
turret, and the head can tilt in two directions, unless you have everything
at dead right angles, the setting won't be proper because of the compound
angles you generate. You begin by squaring the turret with the saddle
ways and go from there. When you have everything in proper attitude, you
can then dial the angle from a sine plate or bar, which must also be dialed
true before use. Lots of setup and overkill, but that's how you set the
angle properly. Some folks go by the marks and call it good enough.
Thanks for the input. Although I didn't mention it, I did assume that the
head would be trued before making any adjustments. Using a sine bar means
using gage blocks too, right? I don't think I can justify buying a set for
just one project but I'll see if I can find some imports on sale. I've
never used a sine bar but I understand the concept. How about a "Reader's
Digest" version of how to calculate the height needed for an angle you want
to set it for?
As for James' idea about inspection angles, do you stack them to get an
angle when there isn't one made for the angle desired?
You can get a "spacer block" set cheaper than gauge blocks, sometimes
as low as $25 for the set. They are round and have a threaded hole in the
center, so you can stack them up on a long set screw, which is provided.
I can't imagine trying to wrestle some item onto a sine bar supported by
a wobbly stack of gauge blocks! Doing the same with a set of clamped-
together spacer blocks is definitely better, but still a bit tricky.
Wobbly stack of gage blocks? You apparently have never worked with
them. While I'll openly admit the possibility of them tipping over, gage
blocks that are properly wrung together are hardly wobbly. Further, the
square variety have tie bars to prevent them coming apart. The only real
issue is the stack tipping over, and you'd face that with any spacer unless
it had a very broad base.
I do agree with your assessment of spacer blocks, however. Unless the angle
desired is ultra critical, a spacer of proper length could be easily made
from a piece of solid stock for any particular setup. No real need to buy a
set of gage blocks, although they are a nice addition to any shop. Missing
the length of the spacer by even a thou translates into such a small error
that it's highly unlikely that a mill would have the necessary precision to
make any difference.
The ultimate way to get around the wobbly situation is to work with a sine
plate instead of a bar.
That part's pretty easy. All you do is refer to trig tables. Considering
I have no mathematics aside from general math behind me, I'll leave it to
the mathematicians to describe the process. I'm pretty clumsy at it.
dberryhill wrote in message ...
A sine bar has a top plate mounted on two round bars (one pivots).
The important number is the center to center distance of these two bars
along the top plate.
Five inches seems to be standard.
The formula is (distance between bars) times (the sine of the angle desired)
equals (the height of the stack).
for 22 deg
sine of 22 = .3746
5 x .3746 = 1.873
You need a 1.873 inch stack to get 22 deg.
Paul K. Dickman
While others have described the methods for setting the angle on the head,
sometimes it is easier to leave the head square and set the angle of the
work. Small stuff can be set on top of a sine bar in the vise, larger stuff
can be held in a sine vise. ( The vise tips and is clamped in place.)
Often the setup depends on how much work is needed at an angle and the
precision required. As an example if you were making an injection mold with
rising detail a high degree of precision is required, but if you were making
a vacuum forming mold and needed a draft angle so the part would release you
could probably just eyeball the protractor scale and be fine.
Yes you stack to get the proper angle. the sets usually come with
1 2 3 4 5 10 15 20 25 30 degree blocks. check out the KBC tools online
catalog page 580.
There is a realy nice Brown & Sharpe set that has recesses to hold
the part or other blocks. not cheap thought :-)
As Harold says about lining things up, but there are actually 3 axis
to align, depending on the model, the Ram can revolve on some machines
as well as the rotation and tilt of the head. For most application most
people rarely move the ram alignment. Easily checked by sticking an
indicator holder on the table, and indicate the inside of the dovetail
on the ram by moving the table in and out. They align the two axis on
the head and go from there.
as a relatively novice machinist with a bridgeport i wonder is there a
book with all these simple setups and techniques explained ?
i know there is a vast amount of knowledge here on the group but i feel
silly asking simple questions that everyone has probably answered a
million times. kind of a "milling for dummies" explaining techniques
for tramming, clamping, angle setups,etc etc etc.
i manage to do everything i try to do, but i'm sure there is a right
way and a wrong (less precise) way
: Using a sine bar means
:using gage blocks too, right? I don't think I can justify buying a set for
:just one project but I'll see if I can find some imports on sale.
Unless you need extreme accuracy, a set of adjustable parallels and a
micrometer work just fine.