lathe trouble

had to quit my project today…was getting way angry to continue working.

here’s the deal….i had machined most of 5 valvebody’s as i knew i would probably mess one or 2 up…that took me about 3-4 hours to do, which is ok since i had to figure out some stuff as i went along.

came to the external 18mmx1.5mm that goes into the bottle…gearing ratios in the manual is not very precise…for 1.5mm thread….after a bit of googling in found the right ratio’s changed gears and started to cut as i allways do adding .002″ pr cut…..

first cut ran perfectly, with a nice clean cut…i thought it was going to be easy….second cut looked slightly off but i find that sometimes it takes a couple cuts to make it look right….third cut strips the thread…arghhhh…WTF….check threading dail…its as its supposed to…check gears if it can skip or something…all is good

cutting tool is firmly mounted…cant see that doing it…..

im using cutting oil as supposed to….

i tried cutting in some aluminum just to check….and i simply dont get whats going on….

anyone have a clue …..as to what is going on….lathe is one of those minilathe from cummings

martin777

Participant

September 10, 2007 at 10:04 pm

VERY IMPORTANT!!–Are you set up to advance the COMPOUND ONLY (set at <30 Deg.) or are you plunging the tool straight in with the cross-slide? Plunging the tool straight in is NOT the preferred method but the most commonly used—Lookie here!!!–>http://www.mini-lathe.org.uk/threading_tool_angle_advance.shtml
I always take the backlash out of the lead screw by bumping the carriage handle CW (when threading R to L) BEFORE I make a pass. Might help. The pictures kinda look like there’s “chatter” at the tool. I snug ALL the gib screws before turning-could help with chatter. How deep are your cuts? I only go 0.002″ per pass. Spindle speed ~50 RPM ? I have 2 good ~1Hr. videos of treading/stuff on a mini-lathe and I would gladly mail u copies if you like.
Here are some good links to mini-lathe stuff—>

http://www.homestead.com/tool20895/jose7x10taig.html
http://www.varmintal.com/alath.htm
http://www.mini-lathe.org.uk
http://www.gadgetbuilder.com/index.html
http://www.mini-lathe.com

There is SOOOO much to read/learn–
Good Luck 🙂

shadoh

September 10, 2007 at 9:44 pm

Cyg, did you say you always use the number 1 on the threading dial? I know on my machine that allot of times I can use any number on the dial as long as I us that same number for each pass. There are some threads though that you can only use certain numbers on the dial. Is it possible that its one of those?

Your first example is how I cut threads as well. Motor running all the time and using the threading dial.

I also often cheat and hand turn my lathe to cut threads. Its a tiny bit slower to make them this way but I know that they are perfect everytime I do them. I keep saying Im going to make a crank handle that I can put on the shaft to make this easier but I never manage to get around to making one. It usually leaves a pretty good size blister on my hand if I do allot of them this way.

dragonflyslayer

September 10, 2007 at 9:06 pm

Thank you ..
I am sorry for talking a whole bunch of nothing…
But if it is the finish of the material he is tripping on in my schooling with the DOD that area had to do with Feeds and speeds among metals and their properties.
But if it is a size and fit issue that would have to do with measurements and tolarences usually within 2 to 5 thousnads but measure the piece your trying to duplicate and keep it in the ball park?

It’s right uner his nose man….
I know it is…
God he was giving me a NAVY flash back .. 😯

😆

September 10, 2007 at 8:24 pm

Dragonfly,

He’s making new valve bodies for AF rifles.

September 10, 2007 at 8:23 pm

With great respect.. I am not too sure what your exactly trying to machine. But iworked in the NAVY on board USS Tripoli LPH 10 in a machine shop and I knew some great journeyman machinists. I know it has to do a lot with Feeds and speeds on turning out metals and their properties.
There is just so much to know in this.
So maybe stick to basics and depending on the material your planing to use and make sure the feed and speed is correct and …well I don’t even know what it is your trying to turn out. But I do know if the cut is jacked up or rough it has to do with the feed and speed of the material and or your cutting tool. Do you have a grinder and can you sharpen your cutting bit?
Just found this post interesting and wanted to help if possible but I don’t even know what your trying to turn out.

Best of luck to ya. Don’t let it spin your wheels now…
Just try to find out some answers perhaps regarding the material your using and feeds and speeds.
I am no journeyman but I have turned a few things and milled a few things and I know feed and speed is a major factor in success.
For the cutting tool and the material being cut.
Metals and their properties….

The answer is probably right in front of you. And if it is something your trying to replace take,you may want to take measure what your trying to fit it to. because personaly if there is a set constant for that part and what your going to fit it to may have friction wear to it that woud simply be a different fit…
So I know it is good to check and take a caliper to what your goint to replace or fit something with…
alright then…

I would like to know more… Sorry if I have butted in wrong… I wish I had the answer for you..
Wow..ths is the first machine trivia I have heard someone question..

8)
“Don’t give up… find out why… then go from there ..
Then your probably going to find the results you need.

Marc

cygnus-x-d82

September 10, 2007 at 8:01 pm

2 out of 5 bodies…are scrap…i used to test some different ways of doing it

normally i would have the lathe running forward…..wait for dial to reach one and engange the leadscrew….and do a pass….let off the leadscrew roll it back and repeat whith the motor spinning forward all the time…and then just wait for dial to reach 1 …repeat

now i have the lead screw enganged all the time….that way i dont have to use the dail….i cut…stop motor…move tool out reverse….tool in…forward….

alot more hazzle than just engageing the leadscrew…..but it works….

3 in front is ok…..back left the thread is canted as when i used a die to try fix the thread was canted a bit…back right the tops of the thread is fucked, will screw into bottle ok…but when dealing with hpa…i want it to be perfect, and since the thread is undersized cause of the offset cut

September 10, 2007 at 7:12 pm

How long is it since you last cut a thread? Just wonderng if maybe your missing a step?

I’d watch that DVD you bought again and make sure…

If that doesnt help… then maybe its just bad karma… 😛

September 10, 2007 at 6:35 pm

It sure sounds like the gearing or the gear that drives the crossfeed. Off hand I would say gearing as you can check the crossfeed easy enough. Try it out on some scrap until your sure its right. I would hate to see you lose more valve bodies.

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