1 in 12 taper?

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EOsteam
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1 in 12 taper?

Post by EOsteam » Mon Jan 11, 2021 11:51 pm

I'm working on the pedestal binders for the 4-8-4 Northern project. I have to cut a 1 in 12 taper on the frame of the locomotive and also match that to the pedestal binder. The pedestal binder will have the female 1in 12 and the frame will have the male. How do I set up the milling machine to mill a 1 in 12 taper? The tab will have a height of .375" and of course the hypotenuse of that triangle that forms the taper is .3762" The angle of a 1 in 12 taper is 4.76 degrees.
My wife the math teacher is finally getting me back up to speed with trig. It has only been since 1981. We have the math figured. It's just the setup on the milling machine that eludes me.I can submit a simple hand drawn sketch if that will help.

As always, your help is most appreciated.
Harper

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liveaboard
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Re: 1 in 12 taper?

Post by liveaboard » Tue Jan 12, 2021 10:44 am

I've only done it on a lathe; I just ignored the trig and the degrees, and set the compound slide at [in my case] 5:1 for a 10:1 taper.

I did that by putting a dial gauge on it against a test bar, and counting off 10 revolutions of the compound screw; when the dial gauge showed a reading equal to 2 x the pitch, then the compound was correctly set.

It took a while.

This was to cut a propeller shaft to fit a propeller with a factory made bore.

I took the toolpost off to make room for the dial gauge base.
propshaft setting compound angle witha straight shaft.jpg

John Evans
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Re: 1 in 12 taper?

Post by John Evans » Tue Jan 12, 2021 12:33 pm

Sine table or tilt table.
www.chaski.com

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rmac
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Re: 1 in 12 taper?

Post by rmac » Tue Jan 12, 2021 4:16 pm

I'm not familiar at all with locomotives, so I don't know what the parts you're talking about look like or what exactly you have to do with the milling machine. So a sketch would certainly help me.

What might help you (maybe) is this video, which shows a clever way to make accurate angle cuts on the mill:

https://www.youtube.com/watch?v=lDwAzcSUVtI

-- Russ

EOsteam
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Re: 1 in 12 taper?

Post by EOsteam » Wed Jan 13, 2021 2:07 am

Here is a photo of the blueprint. The 1 in 12 taper in circled in red. The pedestal binder itself is relatively easy to tilt in a vise to get the angle but the frame is 5 feet long and will probably require a tilt of the head of the milling machine in order to machine the taper. What is a good way to attain this 1 in 12 taper with the tilt of the head.
Thanks again!
Harper
PedestalBinder (1 of 1).jpg

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GlennW
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Re: 1 in 12 taper?

Post by GlennW » Wed Jan 13, 2021 6:27 am

In that application, It doesn't look like the angle itself is critical, just that the two parts mate up properly. If you tilt the head, and then machine both, they will match. If you tilt one part to mill it, and then tilt the head to mill the other part, they may not match properly. For that method, ust using the graduations on the mill head would probably work out.

If you need a specific angle, I use a Sine Plate and sweep the plate with a spindle held DTI as you would to square your mill head. Sweeping the Sine Plate will give you the correct angle relative to the table. A Sine bar would also work for the intended use here. There are a lot of factors involved though, such as the squareness of both the milling machine ram and the sine plate/bar to the X,Y axes and probably other factors, but I have to go to work now! I'm sure that Harold can fill in the blanks there!
Glenn

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rmac
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Re: 1 in 12 taper?

Post by rmac » Wed Jan 13, 2021 12:57 pm

Harper,

Thanks for the picture. Now I at least know what the problem is. I am FAR, FAR, FAR from being an expert on any of this, but I did have a few ideas that I'll throw out anyway, just in case one of them might actually be a good idea. :D
  1. As Glenn said, if you don't care about the specific angle, but only that the two parts match, tilt the head, machine them both and Bob's your uncle. That might not work, however, if for some reason you can't make the two parts at about the same time. You might also have a hard time duplicating the angle if you ever had to remake one or more of the parts sometime in the future.
    .
  2. Use the technique shown in the video that I referenced to make a gauge that looks something like this:
    chaski_20210113_0002.png
    chaski_20210113_0002.png (15.3 KiB) Viewed 277 times
    Then chuck up a straight rod in the mill, mount the gauge on the mill table with its base parallel to the X axis travel, and adjust the head tilt until the rod lines up (by eye) with the sloped side of the gauge.

    The "by eye" part is a little iffy, but this seems like it would get you really close if you're careful. The other good thing is that you might be able to use the same gauge to set the tilt of the pedestal binder in the vise.
    .
  3. This is similar to what liveaboard described doing with his lathe. Again, chuck up a straight rod in the mill. Then mount a dial indicator on the table so that its plunger is both horizontal and parallel to the X axis travel. Move the table until the indicator contacts the rod and note the reading. Then move the knee up or down.

    If the head is tilted at the desired angle, the dial indicator will change by 1/12 of the knee movement. So if you move the knee 1", the indicator will change by 0.083. Move the knee 2", the indicator will change by 0.167. And so on. Adjust the head tilt until you get it right. As liveaboard said, this might be tedious.

    This all sounds really precise, but the trick would be mounting the indicator so its plunger was exactly exactly exactly horizontal and exactly exactly exactly parallel to the X axis. I'm not sure how you'd do that.
Again, these are just ideas from somebody with very little experience. Hopefully others who know what they're talking about will chime in with theirs.

-- Russ

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rmac
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Re: 1 in 12 taper?

Post by rmac » Wed Jan 13, 2021 3:34 pm

More ideas, first from YouTube ...

https://www.youtube.com/watch?v=rXCxR6MmUbY

... and another from this very forum ...

https://www.chaski.org/homemachinist/vi ... hp?t=75387

... and still more from a different forum ...

https://bbs.homeshopmachinist.net/forum ... ost1049517

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Bill Shields
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Re: 1 in 12 taper?

Post by Bill Shields » Wed Jan 13, 2021 6:48 pm

Purchase a tapered end mill
Too many things going on to bother listing them.

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GlennW
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Re: 1 in 12 taper?

Post by GlennW » Wed Jan 13, 2021 7:06 pm

1 in 12=4.7636 degrees.

5 degree tapered end mills

https://www.travers.com/3-flute-tapered ... tname=SITE
Glenn

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Bill Shields
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Re: 1 in 12 taper?

Post by Bill Shields » Wed Jan 13, 2021 8:55 pm

Get one with the largest SMALL END diameter that will fit in your slot
Too many things going on to bother listing them.

EOsteam
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Re: 1 in 12 taper?

Post by EOsteam » Thu Jan 14, 2021 2:33 am

I sure appreciate the help. The 5 degree taper end mill is probably going to be the go to.

This board is a wonderful resource. Thank you all!

Harper

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