# New To Machining With A Question



## boostin53 (Sep 11, 2015)

Hi y'all! This will be a sort of long first post, so please bare with me as I'm totally new to all of this. Been browsing this site for a few weeks now in preperation to begin a new hobby/addiction (machining).  I decided to start small with a Jet BD-920N lathe that I got for a very good price.  The lathe came with a bunch of extra stuff and including some basic tooling. It was too good to pass up considering it was basically free.

I have been practicing facing and reducing on bolts and some scrap 1/2" steel bar stock of unknown to me metal from work. Today I decided to face and center drill a 12" length. I started by only hanging about an inch and a half out of the chuck, faced and center drilled.  I then put in my live center on the tailstock and extended the work piece out.

I began turning down the steel to my desired diameter of .415".  While confirming measurments during the turning process, I noticed some variations on the measurments. The front half measures in at .416" while the back half measures in at .427".  I then thought maybe I didnt turn in my tailstock enough to support my work, causing some slop. But it was good and tight.  So to wrap this essay of a post up, what can I do to eliminate this and get the same diameter on the entire length I'm turning?


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## Bill C. (Sep 11, 2015)

What does the middle measure?  Depending on your lathe it could be your tailstock is not truly centered. It could the offset is passed center cutting a taper.  Also for stock that long take light cuts to keep the it from flexing on you.  Good to learn you are practicing on bolts and scrap steel.


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## T Bredehoft (Sep 11, 2015)

Most if not all tailstocks have an adjustment for centrally horizontal. Your first thing to do is to chuck a short piece of stock/scrap in the chuck and turn a point on it. The finer the better. Then, bring the tailstock with a center in it up to about 1/4" away from the point you just made. Clamp the tailstock to the lathe, put a bit of snug on the tailstock spindle and crank it up to almost touch the point. Look at the two points from above, and adjust the tailstock so that it as good as you can get it.  While there, check for vertical alignment point to point. There's not a lot you can do about vertical alignment, but it should be good. 
Next, cut a piece about five inches between chuck and tailstock. Take a skin cut and measture at each end. If the right end is off .004, move the tailstock (use an indicator) .002 in the correct direction. (If it's big on the right end, move the tailstock toward you, if it's small, move it away. 
Your twelve inch piece is too long to not flex when you're cutting it, it needs a steady or follow rest to support it from the cutting pressure.


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## Wreck™Wreck (Sep 11, 2015)

boostin53 said:


> So to wrap this essay of a post up, what can I do to eliminate this and get the same diameter on the entire length I'm turning?



Exactly how much deviation from the desired dimension is too much? If you require .003" error on a .415" Diameter 9 inches long with a nice finish, this is not going to happen in a conventional lathe, this would be asking a lot of a box tool as well.


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## boostin53 (Sep 11, 2015)

Wreck™Wreck said:


> Exactly how much deviation from the desired dimension is too much? If you require .003" error on a .415" Diameter 9 inches long with a nice finish, this is not going to happen in a conventional lathe, this would be asking a lot of a box tool as well.



I can live with a fair amount of error. I'm just trying to get my machine to cut as accurate as possible. The closer to my target dimensions, the better. And I didnt think about the tailstock being off center. Im not able to get to my lathe at the moment, but I will do what you guys advise as see where Im at.

So in reality, what type of tolerance is to be expected on these lathes? Like I said, I can live with error. Just curious to know.

Edit: I would also like to see consistent dimentions across the work piece. Regardless if Im off of my target dimention.


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## T Bredehoft (Sep 11, 2015)

On a four inch piece, chuck on one end live center on the other, from 1/2 inch to 2 1/2 inch diameter you ought to be able to hold .0005, maybe better, any better than that, you might want an OD grinder.  Yes, better is possible, when I need better I work with a block of wood behind some 400 paper and take my time.


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## JPigg55 (Sep 11, 2015)

Here's the links to a couple MrPete222 vYoutube videos that might help with checking your tailstock alignment.








 
He has a ton of videos well worth watching.
Somewher on this forum is a list of the videos and links, not sure where it moved to.


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## Charles Spencer (Sep 11, 2015)

Firstly I agree to check the alignment of the tail stock.  I would do this by placing a center in the head stock and moving the tail stock with the center in it up to it and aligning them by eye.

I quote http://www.smithy.com/machining-handbook/chapter-3/page/20

"The most accurate method of checking alignment of centers is by mounting the workpiece between centers and taking light cuts at both ends without changing the carriage adjustments. Measure each end of this cut with calipers or a micrometer. If the tailstock end is greater in diameter than the headstock end, the tailstock is moved toward the operator. If the tailstock end is smaller in diameter than the headstock end, the tailstock is moved away from the operator. Take additional cuts in the same manner after each adjustment until both cuts measure the same."

Also there might be a runout issue with the chuck.  I generally like to turn down stock between centers.  If the centers are aligned properly it tends to be quicker than trying to minimize runout from the chuck.


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## boostin53 (Sep 13, 2015)

So as it turns out, my tail stock was off by a few degrees. I dont know how much since the ink on the dial indicator plates are worn off. Took some trial and error to get it centered. Also, my three jaw chuck had a fair amount of run out. Removed the chuck to clean and inspect the mating surface. The previous owner managed to slightly ding the chuck where it mounts to the headstock. Took a file to it and lightly removed material until it sat flush. Im now skinning material evenly across my stock. 

Now another problem. I just found out i wasnt given the keys for the 4 jaw, and its an inverted key unlike the 3 jaw i have. Using a pair of sockets and wrenches for now. Now i need to figure out how to broach without the proper tooling so i canmake myself two keys. Tried searching online with no luck. Either my google-fu sucks or im missing it.


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## Charles Spencer (Sep 13, 2015)

If you don't have it, the manual is here:

http://content.jettools.com/assets/manuals/321376_man_EN.pdf

It appears Jet still sells this model:

http://www.jettools.com/us/en/p/bd-920w-belt-drive-bench-lathe/321376

And they will sell you a new chuck key (part # BD920N-FCK) for $11.74 here:

https://parts.jettools.com/SearchResults.aspx?s=BD920N-FCK


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## boostin53 (Sep 13, 2015)

I have the manual. I dont know why i didnt just look in the back and get the part number for the chuck key. Thank yoi for the help guys!


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## kwoodhands (Sep 29, 2015)

boostin53 said:


> Hi y'all! This will be a sort of long first post, so please bare with me as I'm totally new to all of this. Been browsing this site for a few weeks now in preperation to begin a new hobby/addiction (machining).  I decided to start small with a Jet BD-920N lathe that I got for a very good price.  The lathe came with a bunch of extra stuff and including some basic tooling. It was too good to pass up considering it was basically free.
> 
> I have been practicing facing and reducing on bolts and some scrap 1/2" steel bar stock of unknown to me metal from work. Today I decided to face and center drill a 12" length. I started by only hanging about an inch and a half out of the chuck, faced and center drilled.  I then put in my live center on the tailstock and extended the work piece out.
> 
> I began turning down the steel to my desired diameter of .415".  While confirming measurments during the turning process, I noticed some variations on the measurments. The front half measures in at .416" while the back half measures in at .427".  I then thought maybe I didnt turn in my tailstock enough to support my work, causing some slop. But it was good and tight.  So to wrap this essay of a post up, what can I do to eliminate this and get the same diameter on the entire length I'm turning?




Center drill both ends and turn between centers. Turn to dimension about 3" from the TS end. Turn to about .002 full til you get about halfway.Reverse the part,turn to dimension .The 3" turned to dimension is to clear  the lathe dog after reversing the part.I leave the part .002 full so the last pass at slow carriage feed leaves a smooth surface.
As mentioned a rest set up in the middle will help with deflection.If the live center is turning ,then the TS is set okay.
It would be rare if the TS is centered for height and laterally correctly.Turning between centers eliminates most of the problem.With our lathes .415/.420 would be considered good.

mike


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## don00298 (Mar 15, 2016)

Hi everyone, glad to be a member now. I purchased a 13" south bend in December, this old lathe was built in the mid to late 40's I think, and is in fare condition for its age. I also have a Maxmill (1970) which is a Japanese version of a Bridgeport vertical mill that I've been using since the early 80's, that being said I have some knowledge of machining metal. This is my first lathe and at the same time the first lathe I have ever touched or used. My question is when I try to face the end of my work the apron tends to move side to side (chuck to tail stock) therefore the cut is not true, is there a way to lock the apron (handle) in order to prevent this? Is there an adjustment to increase the horizontal drag or is this a problem with the lathe itself? Any suggestion much appreciated.


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## T Bredehoft (Mar 15, 2016)

Somewhere on the saddle (that part that slides left and right with the tool on it) is (generally on the right side) a generally square end of a bold. This should lock down the saddle, to keep it from moving left and right. There are screws across the back (with nuts on them) that adjust what are called "gibs" (pronounced like the guy on NCIS) these are to adjust the friction between the saddle and the 'ways', the rails the saddle slides on. Be aware than any old lathe may have wear under the gibs where the lathe is used most, near the chuck, and if the gibs are adjusted snug at that point they may be tight as you move the saddle to the right. 

End of Saddle 101


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## TC0853 (Mar 17, 2016)

First I would set up a dial indicator and check for runout in your 3jaw Chuck. That would account for your work getting small the closer you get to the headstock If you suspect your tailstock is out, go to this YouTube link
https://m.youtube.com/index?&desktop_uri=/#/watch?v=utZVv7QvRt8 . If that won't open it up just do a search for lathe tailstock alignment tool by Ray Caniglia. He put that segment up at least a couple years ago, it's  a nice little easy tool to make, and you'll need a starrett 196 back plunger dial indicator, they're on eBay all the time. That way, instead of checking the tailstock by eye you can dial it in to .001" or less. IMHO! Also, like someone mentioned earlier the more of your work in the Chuck, the truer it will be. Good luck!


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## Wreck™Wreck (Mar 17, 2016)

TC0853 said:


> First I would set up a dial indicator and check for runout in your 3jaw Chuck. That would account for your work getting small the closer you get to the headstock



Actually it doesn't account for this, the spindle will describe a circle on the cut surface regardless of how much run out a chuck, center or collet has, it will not cause a taper condition. The turned portion of the material will not be concentric with the portion held in the jaws/collet however.


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## stupoty (Mar 17, 2016)

I wanted to get a nice slip fit for a shaft to run in bearings with a 5mm id , it was only about 1.5 inches long though, i ended up doing it unsuported and correcting areas that flexed most manualy using a shear tool then a file then blended them with abrasive cloth paper (i have some nice 1" wide stuff on a roll) i managed to get it withing less than a couple of tenthes all the way along.  Bigger lengthes would take longer it wasn't a quick process to be fair.

Stuart


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