Proper way to layout round stock undercutting using a parting tool

tbussi · Dec 10, 2019

I've seen some forums where hermaphrodite calipers are used for marking round stock in a lathe while it is rotating. Having to set it with a rule and using layout dye prior to marking.
I've also seen some discussion about using a dial caliper (or perhaps a vernier caliper) to mark the same. Although over time this may damage the caliper.
Also have seen discussion about using a surface plate with a height gage to mark it up as well.

My question is: Is there a more correct way to do this especially when teaching a shop course to students?

Dumpster_diving · Dec 10, 2019

Hermaphrodite calipers are cheap. No penalty for degrading the tips (that can be resharpened on a grinder).

Calipers are slightly more expensive, though not uniformly so. Quality electronic calipers are expensive. Dial calipers less so. Verniers still cheaper. If you're willing to treat them as semi-consumable nothing wrong with using them for the occasional rotating layout lines.

Height gage on a surface plate is excellent for flat stock. Not as easy to scribe a layout line on bar stock vertical on the surface plate.

So short answer is teach all methods and their pros and cons.

MrWhoopee · Dec 10, 2019

Touch off on end of part with parting blade and set zero. Crank in specified distance plus blade thickness. With part rotating, bring tool in to barely touch. If no means of measuring carriage travel, use scale, caliper or depth mic to measure from end of part to edge of blade.

DMF_TomB · Dec 10, 2019

tbussi said:
I've seen some forums where hermaphrodite calipers are used for marking round stock in a lathe while it is rotating. Having to set it with a rule and using layout dye prior to marking.
I've also seen some discussion about using a dial caliper (or perhaps a vernier caliper) to mark the same. Although over time this may damage the caliper.
Also have seen discussion about using a surface plate with a height gage to mark it up as well.

My question is: Is there a more correct way to do this especially when teaching a shop course to students?

.
with cnc, parts not normally have layout lines and center punch marks
.
sure manual machining might need to do depends on what shop equipment you have. if you got rotary table many times still might not need to layout stuff

NC Rick · Dec 10, 2019

My friend with a “real shop” laughs at me when I talk about “layout”. I still do it on my manual machines (the only kind I have) to save myself from often made mistakes. I still use a dial indicator on the carriage (still miss my old travadial...) a DRO should be part of any real machine these days I suppose. I don’t have one for my lathe. It has got to be good to teach how to do layout as is teaching manual drafting. I remember an exercise in school where we used two plates, three dowel pins, a center-punch, calipers, reamers and dimensions to lay the plates out to mate. I never had to do that again but lessons stuck and it is a fond memory.

Mtndew · Dec 10, 2019

tbussi said:
marking round stock in a lathe while it is rotating.

My question is: Is there a more correct way to do this especially when teaching a shop course to students?

First of all, if you're teaching students, I would hope that the spindle is in neutral and it's only moving by hand.
There are many ways to do this, none of them wrong.
Have them use a 6" scale and a scribe.
Or
Put a sharp corner tool (HSS preferred) in the tool holder, touch off the face of the part, set the readout to zero and move over the desired amount and scribe it that way.

tbussi · Dec 10, 2019

tbussi said:
I've seen some forums where hermaphrodite calipers are used for marking round stock in a lathe while it is rotating. Having to set it with a rule and using layout dye prior to marking.
I've also seen some discussion about using a dial caliper (or perhaps a vernier caliper) to mark the same. Although over time this may damage the caliper.
Also have seen discussion about using a surface plate with a height gage to mark it up as well.

My question is: Is there a more correct way to do this especially when teaching a shop course to students?

Thanks for all of the great replies. Helped me out tremendously! Thanks everyone.

MrWhoopee · Dec 10, 2019

NC Rick said:
My friend with a “real shop” laughs at me when I talk about “layout”.

Layout is a great way to make sure you don't make a mistake on the dials/DRO. If I walked up to Fred with a milled part I'd scrapped, the first question was "Did you lay it out?"

Limy Sami · Dec 10, 2019

Use a bed stop and blocks - I've an old set*** of gauge blocks I keep by the lathe especially.

*** By which I mean they're within 2 or 3 10,000ths on an ordinary mic.

litlerob1 · Dec 10, 2019

I want to know what "hermaphrodite calipers" are. Sounds weird.

R

MrWhoopee · Dec 10, 2019

litlerob1 said:
I want to know what "hermaphrodite calipers" are. Sounds weird.

R

https://www.msdiscounttool.com/cata...C_XN_i_vpxw4is0Cwxt2D4f3rOzP_glhoC-14QAvD_BwE

mark costello · Dec 10, 2019

Just an old timey way it was done around 1912,

FIL knew the Guy.

mike 44 · Dec 12, 2019

My grandfather had two of these calipers that look like he may have made them. Small one is 4" long and the other about 6/7" long. On the leg that rests on the face end there is a small notch ground in.
I asked him what the notch was for, he showed me. The notch keeps the leg from sliding off the faced end.

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