zarembak (09-13-2019)
zarembak (09-13-2019)
Explanations of this technique of selecting blocks always seem to gloss over the fact that, even with the 81 block set, there are stack heights that cannot be constructed...
As an example, consider 5 * sin (1.25) = 0.10907 ~= 0.1091
0.1091 - 0.1001 = 0.009 and there is no block of this size.
This persists until the second digit to the right reaches 5, e.g....
0.1501 - 0.1001 = 0.050 and there is a 0.05 block.
but
0.15x1 where x is non-zero...
0.15x1 - 0.1001 - 0.05 = 0.00x and we're in trouble again.
Last edited by mklotz; 09-13-2019 at 11:15 AM.
shopandmath (09-13-2019)
Well, if you can throw tenths away whenever they are inconvenient, why are you bothering with them in the first place?
The reality is that the average machinist will probably never need to machine an angle so accurately that he needs to consider the tenths. He really doesn't need gauge blocks except for the convenience when setting sinebars. Just calculate the stack height and machine a block to that dimension.
I discussed stack height errors at length in this post...
Sine bar errors
where I showed that the error equation is...
dA = (1/cos(A)) * dS/L
and provided a table of angle errors corresponding to a 0.001 stack height error...
The error depends on the angle for which the sinebar is set. For:
L = 5 in
dS = 0.001 in
it looks like this:
5 0.0115029
10 0.0116359
15 0.0118634
20 0.0121946
25 0.0126438
30 0.0132319
35 0.013989
40 0.0149589
45 0.0162057
50 0.0178273
55 0.0199784
60 0.0229183
65 0.0271147
70 0.0335043
75 0.0442748
80 0.0659906
85 0.131479
where the first column is the angle, A, in degrees and the second column is
the error in A, dA, in degrees.
Since a sinebar is seldom used for angles greater than 40 degrees, we can
count on an angle error of less than 0.015 deg (0.25 mrad) if we can machine
the stack block to an accuracy of one thou. Unless you're making highly
critical components, don't be afraid to machine your own blocks for setting
the sine bar.
DIYSwede (09-14-2019), shopandmath (09-13-2019)
shopandmath (09-13-2019)
Hi Guys
This video is made for my students that range from this is my first time in a shop to year 3 apprentices
Check out my other videos and give me your feed back
https://www.youtube.com/channel/UC0a...hdlJy1OIlo1Qmw
shopandmath (09-14-2019)
In addition to using an adjustable parallel for the stack, there's another trick if you use a few angles frequently in your work.
Machine a rectangular block of steel such that each of its dimensions corresponds to the stack height needed for the three angles you set most frequently. Store it with the sinebar.
shopandmath (09-14-2019)
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