View Full Version : 5" sine bar questions
02-17-2005, 08:47 AM
Hey guys! I'm still trying to unravel the sine bar mystery (for me anyway). I see how you use one now but am wonering about the plugs for setting height. Once you get into the bigger angles you could use an inside mic I suppose but what about the shorter distances? For real small angles you could use feeler guages I guess but for other angles above that...would you turn to length what you need? You would need measuring equipment for tenths I suppose. And...how many of you actually use sine bars as opposed to a good protractor? You'd have to have an awful pile of guages (plugs) to properly use an sine bar, correct. Thanks!
You'd use a set a gage blocks if you're really worried about precision. You can buy pretty cheap sets of gage blocks that would probably be more than adequate for most people, or you can spend a few thousand bucks for a set of Webber Croblox accurate to a couple milliionths of an inch.
Another alternative is adjustable parallels. Set the height with a micrometer. Again, probably close enough for most work.
02-17-2005, 12:39 PM
The formula for the sinebar relation is:
sin(theta) = h/L
theta = angle of interest
L = sinebar length (5" is typical)
h = stack height
Taking the derivative:
cos(theta) * dtheta = dh/L
dtheta = error in angle for an error in stack height of dh
dtheta = dh/(L*cos(theta))
For small angles (<=5 deg), cos(theta) is approximately one. Then the error in
the angle is given by:
dtheta =~ dh/L
For a 0.001" stack height error (dh) on a 5" bar (L), we have:
dtheta =~ 0.0002 radians = 0.0115 deg =~ 41 arc seconds
At an angle of theta = 30 degrees, we have:
dtheta = 0.001/(5 * 0.866) = 0.0132 deg =~ 47 arc seconds
So, we can say that, for a 5" sine bar, a 0.001" error in the stack height will
give you an angle error of somewhere between 40 and 50 arc seconds - the exact
number obtainable from the formula given above.
To put that in perspective, if you make a 45 arc second error in aiming your
rifle at a target a mile away, you'll miss the bullseye by a foot. In other
words, 0.001" accuracy in the stack height is plenty good enough for all but
the most exacting metrology applications.
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02-17-2005, 12:54 PM
OK, Marv, one more time, REAL SLOW...I understand the part about 1+1=11...
02-17-2005, 01:03 PM
I even got lost on the 1+1 http://bbs.homeshopmachinist.net//confused.gif , and I thought I was fairly good at math, I think carpentary (which I'm use too) uses a different language
Matt in AK
02-17-2005, 01:20 PM
Who's this theta doode? He's been sining & cosing, must be a seriously bad type. http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif
02-17-2005, 01:35 PM
An adjustable parallel set with a micrometer -- which can be done to within 0.001 inch in just a few moments -- makes a dandy riser for a sine bar if you can live with the residual angular error.
To generate an angle of 45 degrees with a 5-inch sine bar, the riser should be (5 inch x Sin 45 Degree) = 3.5355 inch. Making the riser 0.001 inch oversize increases the generated angle to 45.016+ degrees . . . less than 1 arcminute of error.
To put that into perspective, the vernier scale on a machinist's bevel protractor is graduated to read in 5 arcminute increments.
You should also remember that the angle is determined by the distance one roll is set above the other; small angles can be generated by using risers of the appropriate different thicknesses under both rolls. This allows you to set small angles very precisely using gage blocks. As a simple numerical example, using a 0.1000 inch gage block under one roll and a 0.1004 inch gage block under the other roll theoretically tilts the sine bar by Arcsin [(0.1004 inch - 0.1000 inch)/5.000 inch] = 0.0046 degree = 16.5 arcsecond.
Do note that I inserted the word "theoretically" in my previous sentence. Why? Because the residual errors in the sine bar itself -- remember the ad "rolls to size within 0.0002 inch and bar surface parallel to center of rolls to within 0.0003 inch"? -- bring the "noise floor" of the measurement up to the level of my example.
02-17-2005, 03:29 PM
One thing to do if you have a 5" sine bar or plate is pick up one of the solid cage bloks that are made for setting at a variety of angles by resting the roll on the selected flat.
02-17-2005, 05:51 PM
I rarely use sine bars at work, they are mostly used for setting up for precision operations like grinding. Get a set of angle blocks and that will be good enough for 99 percent of the jobs you do. Using a protractor and scribing a line to mill to also works fine for most jobs. I mean if you want to use a sine bar to set up for a milling job it will work it is just a bit of a overkill in my book and takes added time and I bill by the hour. A good sine bar is a precision made guage and I would be pissed if I saw someone using mine on a mill.
02-17-2005, 06:27 PM
Never thought about using my compound sine chuck on the mill (limited magnetic holding power) but it sure allows fine work on the surface grinder. Used it just yesterday to machine an automotive wheel spindle (E-type Jag) so that the spindle face had the same 0.0057" runout as the disc carrier, with both runouts parallel. This provided a reference to true the disc carrier. And it took only two or three minutes to set up.
02-17-2005, 07:07 PM
Holy Smoke!!! That's a lot of info! A bunch of things I never thought of also. Like shimming the opposite end to split "hairs"...good trick. And I like the adjustable parallel trick too. As far as the math goes...I think I'll just cheat and open the Machinery's Handbook to all the pages they have with guage block heights for any given angle...LOL! I'm sure some of you guys who use these all the time think it's no big deal but to my mind these sine bars seem like kind of an archaic way to set up angles. Is there not a better way or are we talking a ton of money for any other way? I have to get all this stuff figured out. I never know from one day to the next what is going to walk throught the shop door any more. Thanks to all!
02-17-2005, 07:22 PM
Just for information sake, I wrote a little visual trig calculator program about 10 years ago. It's really easy to use. Maybe some of you will find it usefull ...... maybe not. If you want it, shoot me an email.
02-18-2005, 02:17 AM
Wow its like that marv guy should be building rockets or something. I go on my 5 dollar calculator punch sine the angle times the length of the sine baar roller to roller.equals. I think thats it. Simple aint it.
02-18-2005, 05:17 AM
I use a sine bar every time I use the surface grinder for a precision angle and it's important. For milling it usually doesn't matter as much. Most of the time I use the angle blocks I ground years ago. The angle blocks will be your best bet for the majority of your work. But a cheap set of gauge blocks when you can as you'll use them eventually.
02-18-2005, 01:32 PM
Well, I never actually designed rockets but I did help design inertial guidance
systems for ICBMS. Does that count?
Doing an error analysis of a sine bar (per my previous post) is no different,
though much simpler, than an error analysis of a gyroscopically stabilized
platform. Once one has the equations describing the system, it's largely a
matter of 'turning the (mathematical) crank'.
And yes, any machinist who is still looking up trig functions in his
copy of MH is wasting his employer's time. A scientific calculator should be
right next to the mike on the workbench.
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02-18-2005, 01:44 PM
Marv, what does a mike look like??? Must be purrcise.
02-18-2005, 07:06 PM
If you don't want to use your gage blocks or spend the $ on getting a set, they sell space block sets (MSC '05 pg 1313) for theis purpose.
[This message has been edited by moldmonkey (edited 02-18-2005).]
02-18-2005, 11:34 PM
Yep,cheap space blocks are the way to go.Feeler gages can also be used to cheat angles.
Yes it never hurts to use trig,but Machinery's is easier at 2:00 in the morning.Plus do you really need seconds of arc on that 68' Chevy intake?
Now,with all that said lets consider the machines we use.That mill drill or even B-port is in no way accurate enough to require the use of precision blocks.Unless you have a jig bore in the basement,buy the step blocks,even Chiwan sets will suffice.
For commonly used angles in the b-port vise,make yourself a jaw out of pre-hardened and ground 4140.Drill and ream a pivot hole near the bottom of one jaw all the way to one side holding a 1/4" off the end to center.Make a rest bar out of something like 1/4 thick x 1/2 wide toolsteel with a matching pivot hole in one end.Then use your sine bar to set the angles you commonly use.Once set drill and ream a second hole on the opposite end through the rest bar and into the jaw.Repaet for each angle.What you end up with is one of those $250 angle setting vise jaws you see in the catalogs.
Course,if your angle doesn't look right,you could just tilt your head a little http://bbs.homeshopmachinist.net//biggrin.gif
02-20-2005, 02:06 PM
[Most HSM don;t need a sine bar and gauge blocks - a vernier protractor is adequate for most stuff and cheap on eBay...