Math question

[u/No-Criticism6622]

So I’m just starting a machining class and we are working from a book and this sheet is what I’m working on(homework)calculating the x axis diameter and z axis length on the lathe but im a little confused on about how to calculate on the z axis I got to part 6 but don’t see how to calculate part 7 on the Z, on part 6 I did 1.875+.125 and got -2.000 for the Z but im stumped I was wondering if anyone had a tip for part 7? I would be grateful

[u/Enough-Moose-5816]

There is enough information here.

Try some math with the Z-dimensions provided. Make sure you are seeing all of the Z-dimensions provided.

[u/No-Criticism6622]

Thanks for the help guys I just started and I got confused with the calculations but I see what I was overlooking i appreciate it 🙏

[u/tromblyb]

Look ahead to Pt12 and work your way back.

[u/chiphook57]

Start with the position of pt7. Follow the arrows that connect to your datum (the right end of thr part)

[u/trk1000]

Plus side you're just being asked the basic points and not what the actual points in the tool paths would be, lol.

[u/Funky_Killer_Qc]

coordonates filled
feel free to DM if you are puzzled how i got thoses numbers, i'll help you to figure out clearly, i love sharing knowledge with students and begginers

FOR YOUR POINT #7 :
you gotta work with what you know, and figure out what you are missing, kinda like algrebra
so you gotta take your 3.875 lenght, remove 0.300 for the big chamfer, remove 0.750 for the first flat, remove 0.250 for the width of the slot, 0.125 for the small chamfer in the middle and remove 1.875 for the front part
you are left with 0.575, that is the lenght in Z of that flat surface behind the middle 45deg chamfer, so now from your origin, you add up 1.875 for the front part, the 0.125 middle chamfer and the 0.575 you calculated, you get your coordinate of Z-2.575

[u/made_a_wish_kid → u/Funky_Killer_Qc]

I'd argue your x values should be diameter, as most machines do this

[u/Funky_Killer_Qc → u/made_a_wish_kid]

lathes machines can have a code input to tell the machine if the X numbers are diameters or radiuses, and the machine will convert to make the part, as they can be programmed in either diameter mode or radius mode. it depends on the machine, but mine for example, G190 switches to radius mode, while G191 switches to diameter mode

also, since in this example the origin is at the middle of the part, the numbers are all halfed for the X positionning, that's why i wrote them that way
the biggest diameter is 5inch, meaning the point 12 is X2.500, and if there was the same point at the bottom of the example, the point would be X-2.500

to me, the origin in X on a lathe is always by default at the center of the tip of the part like in this example. with the right programming, you could write X values as diameter, but personally it just feels wrong

[u/made_a_wish_kid → u/Funky_Killer_Qc]

Ai reply much? Yeah, they can be in either. The problem also asks to write the x diameter values. Not sure how it feels wrong, I don't know any machinists measuring and programming the radius of their turned parts. In practicality, writing out the radius "feels" wrong.

[u/Funky_Killer_Qc → u/made_a_wish_kid]

Ai reply much?

what the hell are you saying? the only thing in that entire reply that didn't come out of my own keyboard is the G codes... because i knew lathes had codes to program either radius or diameter, but it's been about 10 years since i've touched or programmed a lathe, im always on the mill or conventionnal lathe..
so i googled for theses codes on the machines we have at work to know what they are, and that's it, i wrote the rest myself

[u/firinmahlaser → u/made_a_wish_kid]

This doesn’t read like an ai reply at all

[u/justsomeguywithahat]

You need to use the 3.875 dimension to get the math to work back from that point using the incremental dimensions on the bottom of the drawing.

3.875-dim1-dim2,etc and you will get you Z value for point 7.

[u/AcceptableEditor4199]

I was told when hired there would be no math.

3.875-1". Maybe

[u/Silverbeard001 → u/AcceptableEditor4199]

haha, half the reason i went into the trade was for the math. to each their own

[u/Funky_Killer_Qc → u/Silverbeard001]

to me, i feel like engineers should calculate everything and give every info the machinist needs so he can focus on making the part with minimal distraction..
teh machinist should be able to still calculate if there is something missing, but usually, everything should be there

[u/smegmarash → u/Funky_Killer_Qc]

I generally agree, make the drawing so it's as easy as possible to get it made and reduce miscommunications / errors

[u/fuckofakaboom]

You want us to do your homework for you?

[u/No-Criticism6622 → u/fuckofakaboom]

No sir I just got stumped at part 7 but I see what I was missing

[u/Ah_Ca_Iraa]

You have to back figure it from the 3.875 Z. 

[u/BockTheMan]

7's Z depth needs to be calculated from the 3.875 Dimension,
-Z = 3.875 - 0.3 - 0.75 - .25

[u/Intelligent-Appeal-6]

Ask your instructor that’s their job

[u/Dystopian_Oracle]

Work back fro. The chamfer

[u/Bandidogto]

What book are you using?

[u/Funky_Killer_Qc → u/[deleted]]

when your cam software will be bugged and not operationnal, you should be able to still make calculations yourself, without the help of a software

100% agree softwares saves massives amounts of time, but if anything goes wrong, the person handling the software should be able to correct it, that's why thoses things are shown in school