Hey Guys-trig help needed!

mcostello · Post by **mcostello** » Thu Oct 11, 2007 12:44 pm

I am trying to make a thread tool grinding fixture similar to Harolds. I cannot seem to do the math right. If I put a dial indicator touching a mill vise solid jaw and move the x axis 1.000", how much would the y axis move the indicator for 30 degrees? How much for 14.5 degrees? Math program says .577, but this seems around 1/8" off in 3". Like to work closer than that. Thanks for the help.

fourjc · Post by **fourjc** » Thu Oct 11, 2007 2:21 pm

There is a scientific calculator built into Windows.. Click on the calculator icon, if the calculator is in standard mode click on the view menue and select Scientific, make sure that Degrees is also selected..
Now punch in 30 and click on sine, You will get .500", it's that easy.
for 14.4 deg. .25038" Those are the y axis readings for 1"... If you want 2 inches just double those figures... hope this helps..

Rick · Post by **Rick** » Thu Oct 11, 2007 2:32 pm

mcostello

Your calculations are correct !

fourjc

the way mcostello is set up the 1" of travel is not the hypotenuse of the triangle it would be the "run" so he would use tan(angle) = rise/run

The x axis of travel would need to be .886 for .500 of indicator travel and have a 1” hypotenuse along the vise jaw

Rick

fourjc · Post by **fourjc** » Thu Oct 11, 2007 3:55 pm

You are correct... if you set your vise on the milling machine at 30 deg. set you clock at zero, move the x axis one inch the y axis distance would be .577 or 1.732 for 3 inches..
for 14.4 deg. as mentioned it would be .25676 or .77027 for 3 inches.

mcostello · Post by **mcostello** » Thu Oct 11, 2007 8:44 pm

The problem I am having is now this: 1.00" of travel is now set to.577 depth of y axis travel. My Starrett protractor says that there is a .069 error, in 1".It seems to say I am gonna cut a 34 degree angle. My ChiCom swivel vise says 34 degrees also. My US General protractor says also around 34 degrees. I realize the last 2 are not in the same league as the Starrett, but, they are all saying basically the same thing, that I am about to make an extra cut on a used to be good peice of steel.

I am using the same area on fixed jaw with 1" marked off with a marker. I am going the same direction every time to eliminate backlash, I get repeatable results every time they are just wrong.

Could I be using the hypotenuse and not knowing it and getting wrong number?

jutz · Post by **jutz** » Thu Oct 11, 2007 9:56 pm

In your original post, you said you moved the X axis 1". If that is what you are really doing, then your math is correct.

In your most recent post, you said you have 1" marked off with a marker on the vise. This sort of implies you are traversing 1" of distance along the face of the vise, which would be the hypotenuse rather than the X axis travel. If that is really the case, then the Y axis distance would be the sine of 30 degrees.

mcostello · Post by **mcostello** » Fri Oct 12, 2007 11:02 am

I'll go down and try resetting to .500 of y axis travel. For the future is there an easier way to accomplish this task? Some one might have a whiz-bang method that I'll never know if I don't ask. Thanks.

Rick · Post by **Rick** » Fri Oct 12, 2007 11:55 am

As far as an easier way, don't know if it is easier but makes better sense to me and that is to use a sine bar set at the angle against the fixed jaw then you indicate in to zero along the x axis. This method is more accurate and any angle can be achieved very accurately.

Just one of a bunch of ways to do the same thing

Rick

Post by **Harold_V** » Fri Oct 12, 2007 2:08 pm

Rick wrote:As far as an easier way, don't know if it is easier but makes better sense to me and that is to use a sine bar set at the angle against the fixed jaw then you indicate in to zero along the x axis. This method is more accurate and any angle can be achieved very accurately.

While that procedure has the potential to yield good results, it also has the potential to yield bad results.

The problem comes from the placement of the sine bar. Unless it is dead parallel to the ways, error is introduced via compound angles.

Harold

mcostello · Post by **mcostello** » Fri Oct 12, 2007 10:44 pm

Still have not got it nailed down. .500 of y axis movement is yielding a 29.5 degree angle. Checking with a Starrett fishtail also says angle too sharp. Am slowly moving swivel vise to blunt the angle. The only thing I can think of is that I am missing some simple step in the beginning. I am only using the felt tip marker to come back to original starting point, mark centered on dial indicator stem. Dial indicator set to "0", hand wheel set on "0", with backlash taken out. Then moving Bridgeport x axis handle 5 turns- .200 x 5= 1.00, then reading dial indicator

Cannot miscount as dial indicator has a rev counter which verifies 5 revs.
.577 gives 34 degree thread, .500 gives 29.5, going to shoot for the middle.

This does not make sense as to the results, everyones angles must work togheter or parts would be bogus.

Any suggestions. Never had to cut a close angle before.

Post by **Harold_V** » Sat Oct 13, 2007 2:58 am

If your piece is not set parallel to the table when it is machined, because you're cutting a compound angle, the yield will not be the same as the setting. If you're grinding a fixture that creates proper clearance angles along with the threading angle, that's likely what's going wrong. You must deal with the compound angle, not the intended angle.

It might be very helpful for you to provide a picture of what you're doing, so readers can see what you've accomplished. Pretty good chance it will be obvious to someone.

Harold

Post by **GlennW** » Sat Oct 13, 2007 6:19 pm

It's possible that .52357219311850538458256935548949 could give you 30° the way you are measuring it.

Using a sine plate it would be .50"

According to the calculator in Windows, The sine of 30° = .500" per 1". Using the same calculator, the sine of 1° =0.017452406437283512819418978516316 per 1". If you multiply 0.017452406437283512819418978516316 X 30 you get .52357219311850538458256935548949.

I believe that the sine tables and calculators factor in the radius.