headstock stock run out?


John Gallo
 

Hi, my 9a is cutting a taper with a piece of 3/4 steel held in a 4 jaw chuck. Over a 1 inch long cut the dimension near the head stock is consistently .0005" less than a measurement 1 inch further towards the tail stock. This seems excessive but I don't know how to proceed. Are there any other tests I should do to confirm the taper, and if it is indeed off, how do I go about fixing it?


The lathe seems to be in great shape. After I bought it, the only thing I did to it was to take the spindle out and replace the felts. It turned out that it wasn't necessary as the old ones were fine. I didn't touch the shim packs, The spindle runs in bronze bushings and the deflection was .001 when doing the 2 foot bar test.


I really am at a loss as to what to do next, and any advice would be greatly appreciated. Thanks, John.


George Meinschein <george.meinschein@...>
 

John,
Have you made a few real light passes and checked?

Thanks,
George H. Meinschein, P.E.

Meinschein Engineering Consultants, LLC
150 Brittany Drive
Freehold, NJ 07728-1500
Direct Dial: 732-409-0778
Cell: 732-580-1736
Fax: 732-358-0369
www.meinscheinengineering.com

On Mar 5, 2017 12:32 PM, "johnnyblock1@... [SOUTHBENDLATHE]" <SOUTHBENDLATHE@...> wrote:
 

Hi, my 9a is cutting a taper with a piece of 3/4 steel held in a 4 jaw chuck. Over a 1 inch long cut the dimension near the head stock is consistently .0005" less than a measurement 1 inch further towards the tail stock. This seems excessive but I don't know how to proceed. Are there any other tests I should do to confirm the taper, and if it is indeed off, how do I go about fixing it?


The lathe seems to be in great shape. After I bought it, the only thing I did to it was to take the spindle out and replace the felts. It turned out that it wasn't necessary as the old ones were fine. I didn't touch the shim packs, The spindle runs in bronze bushings and the deflection was .001 when doing the 2 foot bar test.


I really am at a loss as to what to do next, and any advice would be greatly appreciated. Thanks, John.


Jim B. <btdtrf@...>
 

Did you take the twist (level)out of the bed? 
Then and only then center the tailstock. 

Jim B,

On Mar 5, 2017, at 12:32 PM, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:

 

Hi, my 9a is cutting a taper with a piece of 3/4 steel held in a 4 jaw chuck. Over a 1 inch long cut the dimension near the head stock is consistently .0005" less than a measurement 1 inch further towards the tail stock. This seems excessive but I don't know how to proceed. Are there any other tests I should do to confirm the taper, and if it is indeed off, how do I go about fixing it?


The lathe seems to be in great shape. After I bought it, the only thing I did to it was to take the spindle out and replace the felts. It turned out that it wasn't necessary as the old ones were fine. I didn't touch the shim packs, The spindle runs in bronze bushings and the deflection was .001 when doing the 2 foot bar test.


I really am at a loss as to what to do next, and any advice would be greatly appreciated. Thanks, John.


Flash Gordon
 

Hi John,

The bed on your lathe is slightly twisted, not a big deal and very common. Put a thin shim under one of the feet at the tail stock end and bolt the bed to a strong table. Check the taper, if it got worse then move the shim to the other foot.


Ed S


12:32 PM 3/5/2017, you wrote:

Hi, my 9a is cutting a taper with a piece of 3/4 steel held in a 4 jaw chuck. Over a 1 inch long cut the dimension near the head stock is consistently .0005" less than a measurement 1 inch further towards the tail stock. This seems excessive but I don't know how to proceed. Are there any other tests I should do to confirm the taper, and if it is indeed off, how do I go about fixing it?


The lathe seems to be in great shape. After I bought it, the only thing I did to it was to take the spindle out and replace the felts. It turned out that it wasn't necessary as the old ones were fine. I didn't touch the shim packs, The spindle runs in bronze bushings and the deflection was .001 when doing the 2 foot bar test.


I really am at a loss as to what to do next, and any advice would be greatly appreciated. Thanks, John.


John Gallo
 

George, I switched the work to a 3 jaw chuck and took a light cut. There was no measurable difference in the two test diameters. I know I took a light cut when it was in the 4 jaw and it was out .0005. Is it possible that there was some sort of spring in the jaws due to them not being perfectly square to the stock? I know that when truing up work in the 4 jaw with a dial indicator the dial will suddenly jump a few thou when I slacken one jaw. Might this have some thing to do with it? Thanks for your input, John.


George Meinschein <george.meinschein@...>
 

John,
Now that's sounding like more of a 4 jaw chuck problem than a lathe problem to me. Maybe the 4 jaw chuck is not dead square to the spindle. So, the chuck is wobbling on the spindle for lack of a better description. Grinding the jaws is the only way I can think of to straighten this out. I've yet to do that myself on any chuck. Hopefully someone here with the voice of experience will chime in. 

Thanks,
George H. Meinschein, P.E.

Meinschein Engineering Consultants, LLC
150 Brittany Drive
Freehold, NJ 07728-1500
Direct Dial: 732-409-0778
Cell: 732-580-1736
Fax: 732-358-0369
www.meinscheinengineering.com

On Mar 5, 2017 1:39 PM, "johnnyblock1@... [SOUTHBENDLATHE]" <SOUTHBENDLATHE@...> wrote:
 

George, I switched the work to a 3 jaw chuck and took a light cut. There was no measurable difference in the two test diameters. I know I took a light cut when it was in the 4 jaw and it was out .0005. Is it possible that there was some sort of spring in the jaws due to them not being perfectly square to the stock? I know that when truing up work in the 4 jaw with a dial indicator the dial will suddenly jump a few thou when I slacken one jaw. Might this have some thing to do with it? Thanks for your input, John.


John Gallo
 

As it turns out I was over thinking every thing. I was taking inaccurate measurements and looking for off the wall answers. It was indeed a twist in the bed. I fiddled with the leveling leg on the lathe and got the diameters dead nuts over 3 inches. Thanks to every one for their help, and I hope I didn't waste too much of your valuable time with my ranting,John.


William R Meyers <wmrmeyers@...>
 

I am not an expert machinist. I'm a student. Feel free to ignore me. What are you using to measure your .0005" difference? What graduations is your measuring tool graduated in? Do you have enough experience in making close tolerance measurements to actually make a consistant measurement in that range? I am really asking "Are you and your tools really capable of making such a measurement?"

I have been going to school for over two years now and am just beginning to develop the physical skills to consistantly make such measurements. I also have very few tools capable of those measurements, too. When I think I need them I have to use the school equipment. And only one of my micrometers is rated to read in .0001" increments.

What kind of measurement do you get when you cut a 4" length? Oh, and is your surface after cutting smooth enough to trust that .0005" measurement. If you measure the diameter at the same location but 90 degrees around the stock do you get the same reading?

Those are things I have to evaluate on everything I do.

HTH!

Bill in OKC
William R. Meyers, MSgt, USAF(Ret.)

Guard your women and children well,
Send These Bastards Back to Hell
We'll teach them the ways of war,
They Won't Come Here Any More
Use your shield and use your head,
Fight till Every One is Dead
Raise the flag up to the sky,
How Many of Them Can We Make Die!

Heather Alexander, March of Cambredth

--------------------------------------------

On Sun, 3/5/17, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:

Subject: Re: [SOUTHBENDLATHE] headstock stock run out?
To: SOUTHBENDLATHE@...
Date: Sunday, March 5, 2017, 12:38 PM

George, I switched the
work to a 3 jaw chuck and took a light cut. There was no
measurable difference in the two test diameters. I know I
took a light cut when it was in the 4 jaw and it was out
.0005. Is it possible that there was some sort of spring in
the jaws due to them not being perfectly square to the
stock? I know that when truing up work in the 4 jaw with a
dial indicator the dial will suddenly jump a few thou when I
slacken one jaw. Might this have some thing to do with it?
Thanks for your input, John.


Nelson Collar
 

Johnny
I'm no pro but a half of a thousandths on an old machine to me is good. A light emery sanding and knock the half thousand away. 
My opinion
Nelson



From: "johnnyblock1@... [SOUTHBENDLATHE]"
To: SOUTHBENDLATHE@...
Sent: Sunday, March 5, 2017 12:32 PM
Subject: [SOUTHBENDLATHE] headstock stock run out?

 
Hi, my 9a is cutting a taper with a piece of 3/4 steel held in a 4 jaw chuck. Over a 1 inch long cut the dimension near the head stock is consistently .0005" less than a measurement 1 inch further towards the tail stock. This seems excessive but I don't know how to proceed. Are there any other tests I should do to confirm the taper, and if it is indeed off, how do I go about fixing it?

The lathe seems to be in great shape. After I bought it, the only thing I did to it was to take the spindle out and replace the felts. It turned out that it wasn't necessary as the old ones were fine. I didn't touch the shim packs, The spindle runs in bronze bushings and the deflection was .001 when doing the 2 foot bar test.

I really am at a loss as to what to do next, and any advice would be greatly appreciated. Thanks, John.



John Gallo
 

I am using a Starrett micrometer with .0001 graduations. I repeated the measurements enough times to be confident of the values. Also, after testing a 3 inch piece, the difference was pretty much 3 times the results of the 1 inch piece. I certainly am no expert, but this is pretty clear.

Normally I wouldn't worry about a .0005 tolerance. However, the plans for the  small IC engine I am building call for the piston to be no more than .0012 smaller than the cylinder. With an inch and a half long cylinder, a .0007 difference in diameters to start with seems to be too much.

Please feel free to correct me if I am missing some thing here. I am teaching myself and can use all the help I can get. Thanks, John.


William R Meyers <wmrmeyers@...>
 

You have better equipment than I own. My tenths mike is a Harbor Freight. I've tested it against the good set of gage blocks at school and it's accurate to its specified limits, but who knows how long it will last. OTH when I got it, it was better than I am. :) I'm doing better and hope one day soon to be able to justify upgrading. When I got it, a year and a half or so ago, I was afraid I'd ruin a better quality tool. I have since learned better technique, and developed a better feel for the "right" amount of pressure to get a good measurement. Maybe I won't be so ham-handed when I finally get good measuring tools.




Bill in OKC
William R. Meyers, MSgt, USAF(Ret.)

Guard your women and children well,
Send These Bastards Back to Hell
We'll teach them the ways of war,
They Won't Come Here Any More
Use your shield and use your head,
Fight till Every One is Dead
Raise the flag up to the sky,
How Many of Them Can We Make Die!

Heather Alexander, March of Cambredth

--------------------------------------------

On Mon, 3/6/17, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:

Subject: Re: [SOUTHBENDLATHE] headstock stock run out?
To: SOUTHBENDLATHE@...
Date: Monday, March 6, 2017, 2:21 AM

I am using a Starrett
micrometer with .0001 graduations. I repeated the
measurements enough times to be confident of the values.
Also, after testing a 3 inch piece, the difference was
pretty much 3 times the results of the 1 inch piece. I
certainly am no expert, but this is pretty clear.

Normally I wouldn't worry
about a .0005 tolerance. However, the plans for the  small
IC engine I am building call for the piston to be no more
than .0012 smaller than the cylinder. With an inch and a
half long cylinder, a .0007 difference in diameters to start
with seems to be too much.


Please feel free to correct
me if I am missing some thing here. I am teaching myself and
can use all the help I can get. Thanks, John.


ken campbell
 

remember to allow for the bending away from your cutting tool the work piece ... a general rule is that stock should not be unsupported more than 2 to 3 diameters from the chuck . the result of the vector of the cutting force is that the outboard end is larger ...it bends away from the cutter more.

either support the outboard end, or cut at a remedial angle ... according to the tolerance you need . even threading with many passes can show tapered threads ....

wider tolerances can be our friend .... but still unplanned tapered cuts leave us a little depressed .....we know they are there .

so include in your testing kit some known straight ground shafts to sweep when " chucked " .

ken


John Gallo
 

Bill, where did you find a school that teaches machining? I have been looking for one for a long time. By the way, I don't think you have to justify buying a super precision, beautiful tool that will last you the rest of yours and your children's lives if taken care of. If you can afford it, buy it.


Nfwood
 

Go onto eBay and buy one or more, clean them up and learn.  

Nelson W.


-----Original Message-----
From: johnnyblock1@... [SOUTHBENDLATHE]
To: SOUTHBENDLATHE
Sent: Mon, Mar 6, 2017 1:19 pm
Subject: Re: [SOUTHBENDLATHE] headstock stock run out?



Bill, where did you find a school that teaches machining? I have been looking for one for a long time. By the way, I don't think you have to justify buying a super precision, beautiful tool that will last you the rest of yours and your children's lives if taken care of. If you can afford it, buy it.


Rangelov
 

Johnny,
Do not worry about having taper in your piston.

Real pistons are tapered and are barrel shaped. They DO NOT have a true cylindical shape. Generally, the bottom of the piston has the largest diameter, though it isn't truly round.
   
Dimitar
_______________________________________________
2c.
    Posted by:  johnnyblock1@...
johnnyblock1
    Date: Mon Mar 6, 2017 12:21 am ((PST))

<snip>
Normally I wouldn't worry about a .0005 tolerance. However,
the plans for the  small IC engine I am building call
for the piston to be no more than .0012 smaller than the
cylinder. With an inch and a half long cylinder, a .0007
difference in diameters to start with seems to be too much.
 
  Please feel free to correct me if I am missing some thing
here. I am teaching myself and can use all the help I can
get. Thanks


William R Meyers <wmrmeyers@...>
 

Francis Tuttle Technology Center in Oklahoma City. North-West side of town. South-West side of town has Moore-Norman Technology Center. The precision manual machining class cost $1800 last last I looked. The CNC machinist class, which includes the manual machinist class was $4200 IIRC. Don't know how much the course(s) cost at Moore-Norman.

As for justifying, SWMBO has her own little list of things she thinks we need around the house. Gotta give her priority once in a while. Besides, she has let me buy two lathes, a mill, and a shaper in the last few years. Plus a lot of stuff I need for them. She also encouraged me to take the class. I have no complaints. :)

Bill in OKC
William R. Meyers, MSgt, USAF(Ret.)

Guard your women and children well,
Send These Bastards Back to Hell
We'll teach them the ways of war,
They Won't Come Here Any More
Use your shield and use your head,
Fight till Every One is Dead
Raise the flag up to the sky,
How Many of Them Can We Make Die!

Heather Alexander, March of Cambredth

--------------------------------------------

On Mon, 3/6/17, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:

Subject: Re: [SOUTHBENDLATHE] headstock stock run out?
To: SOUTHBENDLATHE@...
Date: Monday, March 6, 2017, 12:19 PM

Bill, where did you find
a school that teaches machining? I have been looking for one
for a long time. By the way, I don't think you have to
justify buying a super precision, beautiful tool that will
last you the rest of yours and your children's lives if
taken care of. If you can afford it, buy
it.