out of round bushing ?

[Petricore]

I have been having the common problem of ends of my pen not ending up round where the hardware meets up with it. At first I thought it was my mandrel, but after running just the mandrel in a properly tightened 60 degree center, running the fingernail test it tests true as true can be. if I shorten it and do one pen at a time its alot better then if I do them both, but still slightly off. I'm mainly doing jr gents right now and am wondering if the bushings themselves are getting out of round, or it maybe he weight of them is what is causing it. the end close to the headstock and tailstock come out pretty good, but the 2 in the middle (where the big spinning mass of metal is) seems to be out of round. Only thing I can figure is either they are out of round, or the weight of the bushings is making the mandrel flex. Has anyone else seen this problem ?

-Linc

 

[KenV]

Theoretically, that is possible, but can be checked with a pencil held on the tool rest (or a direct reading indicator held in an arm on a magnetic base on the lathe ways) to see how much runout is happening on the bushings. Slop in the drilling of the bushing or an off center hole in the bushing is the most likely source of runout.

Due diligence in assuring there is no "cant" in the end of the blanks to "kink" the bushings is a much more likely source of getting an excentric oval turned result. Combined with the tendency for deflection in the mandrel rod under compression with a long length to diameter ratio, a small deviation from true square at the end of the blanks can easily translate to excentric turnings.

 

[Bill Baumbeck]

Likely causes:

1. Excessive forward pressure by the tailstock (causing the mandrel to bend).
2. The brass thumb nut on the mandrel is too tight (causing the mandrel to bend).
3. Spending too much time sanding the blanks (face grain sands much quicker than side grain).

Bill Baumbeck

 

[Russianwolf]

have you checked to make sure you tailstock is in line with the headstock? On mine I had to place a spacer inder one side of the tail stock to geth the drive and tail to line up. If the two aren't aligned it will bend the mandrel once you engage the tailstock. The bend won't likely be permanent but it will effect your pens.

 

[Petricore]

Thanks for the replies. I have checked the head and tailstocks and they are centered to each other. This is while cutting the blank so sanding isnt an issue yet. I barely tighten the brass mandrel so I dont think this is the issue. definately not forward pressure on the tailstock because when I run it without the wood I use the same pressure and its fine.

Ken I will check with a pencil and see how it is. when you say "Slop in the drilling of the bushing or an off center hole in the bushing is the most likely source of runout." can you explain a little more what you mean ? Are you saying I drilled the tube too sloppy, or that the bushing itself was made improperly ? for reference I am drilling onlathe and using gorilla glue that cleans quite easily from the tubes, so there isnt anything in there that would stop it from sitting square. I am rather anal about my reaming to make sure the bushing sit square before turning as well. thanks for the good ideas, I cant wait for your replies

 

[woodbutcher]

Your live center is a likely culprit here. Oneway makes a good one. It will set you back about $90.00. I'm guessing most of the "slop" is on the right side of your pen mandrel.

 

[leehljp]

Get some calipers and measure the bushings. I have done that on most of mine and to be honest, out of about 30 different bushings, I had about 1/3 that are totally perfect or .001 or .002 in out of center. Most are .003 to .004. I have discarded 3 so far that were measureably and visably out of round. At first, I did not check each bushing as I purchased them, only as I used them. Now I check them as I receive them.

It still sounds to me like the mandrel is slightly bent or too much pressure. Do you have a dial guage that you can check the runout? I am not sure about this but it seems that I heard or read somewhere that a flex of .001 (while hand turning) because of slight over tightening of the tail stock - can result in .005 and greater when running.

 

[Brewmeister35]

I fought with this same problem for awhile and have found different reasons for it. All of the responses given so far are possibilities but my most common reason for it is that the barrels were not trimmed square. You can tell if this is the culprit by backing off your tailstock and rotating the mandrel by hand. Stop when the end is at it's highest point. Loosen the nut and twist the barrels 180 degrees and re-tighten the nut. If the mandrel ends up bent down, you need a better way to trim the barrels. Hope I didn't make that too complicated []. Also, you said you don't tighten the nut too tight but it can tighten on it's own while cutting the square edges off.

 

[Petricore]

Thanks again for the feedback, I will double check the bushings and the squareness of the blanks. I am using some homemade inserts to square the blanks, what are you guys using to insure proper squaring ?
Also I'm not sure why my live center could be the problem, its brand new and 60 degree ....

 

[Texatdurango]

Originally posted by Petricore
<br />...Also I'm not sure why my live center could be the problem, its brand new and 60 degree ....

Welcome aboard Linc, you sound just like me a few months back. I had just bought a lot of new tools, started turning and were having the same "out of round" problems that seem to plague almost every new turner.

I was sure that something was wrong with one particular tool or another but after a while, I realized the problem was ME!

When the voices of experience on the forum were politely telling me one thing, I kept saying... "no that's not it, the tool is new" or "no that's not it, I checked".

"New" doesn't mean diddly! Only after spending a few more dollars on a decent live center, did I realize that you get what you pay for! I bought a quality (Sorby) live center and after using it, tossed the piece of junk that came with the lathe, in the trash!

I also learned that I was the culprit when it came to over tightening the brass nut on the mandrel. If the blank is just slightly out of square, over tightening the nut against the bushing just a hair compounds your problem immensly.

I insure blank/bushing squareness by using an end mill with a full tube lenght bushing.

The above comments are intended as helpful, I hope you take them as such.

George

 

[Petricore]

Thanks for the info george. I definitely wasn't meaning to sound snippy with that reply, but going back reading it I see why it came out that way. I bought a 40 dollar live center from craft supply, are these known to be cheap, cause the build quality seems outstanding ! I am seriously leaning towards me doing them out of round because of my reaming not being perfect. Can you explain what an end mill with a full tube length bushing is ? Is that something that works with a collet chuck ?

 

[Texatdurango]

Originally posted by Petricore
<br />...Can you explain what an end mill with a full tube length bushing is ? Is that something that works with a collet chuck ?

After drilling the blanks and inserting the brass tube, I clean up the ends of the blanks with an end mill. You might recognize the bottom setup, it is readily found at most pen supply houses. To me, it is barely adequate since there isn't much width to the cutter.

I use larger diameter end mills* that use a 3/16" pilot. I chuck up a dowel rod, turn it to the inside diameter of a particular tube then drill the new "bushing" with a 3/16" drill bit then glue the bit into the dowel. You can do the same thing with drill stock, I just happen to have hundreds of old 3/16" bits lying around.

As the red lines show in the first photo, using these end mills help insure the blank is square with the ends which the mandrel bushings make contact with. I make a bushing for each size tube I use so changing from one size to the next is quick and easy.

* I use the term "end mills" because some woodworking catalogs refer to these as mills or barrel trimmers. I have always called them counterbores and can probably be found on the internet as such.

Hope this helps some, George

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[Petricore]

Thanks for all the info. right now I have been using my 7mm reamer (3/4" cutting head). I take some wood and drill it to 7mm and glue in a brass tube, then just slip that over the 7mm and ream with that. I have noticed there still is a little room for slop doing it this way. I will have to see if I can get some metal rod inserts I can actually glue the dowels to making it an actual solid shaft. Ill keep ya'll updated.