Boxtool for small shafts

[Mosey]

Anyone know if and where boxtools can be had for turning thin shafts?

I am turning valve stems and want to avoid bending them.

Mosey

[pgp001]

I have one of these.
http://www.chronos.ltd.uk/engineering-tools/2011/small-diameter-turning-tool-sdtt-for-myford-lathes/

Phil

[Ian S C]

The one I can find is by arnoldb Quick 'n dirty box tool,  there is another one somewhere to a design by Tel which is the one I would choose, can't find it, someone will find it.
                                       Ian S C

[Mosey]

Chronos is out of stock on theirs, and the shipping to the US might be too much.
Since I made one of these to turn thin nylon rods, I guess I had better make another, albeit this will be more complex, what with adjustable roller bearings.
Oh, well, stop complaining and get to work.
I would prefer to buy one if it can be found.
Mosey

[jerry kieffer]

Mosey
         I am assuming that you are attempting to machine the valves in one piece.    If so, I can tell you that my personal experience has been that machining valves from one piece of stock has been far more accurate and successful than any other method.     
  All of my personal engines have bores that are under 3/4".     One of the more critical aspects of building these engine has been the accuracy of valve machining in relation to valve sealing that has been critical in proper operation of the engine.
My personal standard on valve seating is that the valve must hold 20 OZ of vacuum for at least 15 seconds.

  Since you have not specified the size of your stems other than small, for this discussion I will assume that they are actually small.

Having said all of that, in my personal experience, follow rests and box tools have not achieved anywhere near the accuracy I am personally happy with when cutting valve stems.     

My personal method for valve stems and other long shafts is as follows.

 (1) I start with metal that will not release stresses and warp during the machining process such as cold roll.

 (2) I then mount a work piece with a diameter to support machining at the far end of the length to be machined.

 (3) From this point, I machine a short section on the end the diameter of the stem to be machined.   (As seen in the
      attached sketch)

 (4)  Steps one and two are then repeated until the length of the stem is cut.

   Jerry Kieffer               

 

[Roger B]

I have been turning my valves from stainless steel bolts/screws. The basic shape is there and they have been forged so the grain flow around the head is good.

http://www.modelenginemaker.com/index.php?topic=2093.15

[Mosey]

Jerry,
The valve stems are to be 0.112" and .75" overall length, and .280" at the head.
Do I understand you to say that the size of the stock to be turned is large? Larger than the final size of .280?
And, you do not support the outboard end of the valve while machining, relying on a large diameter to keep it from flexing while turning??
I am afraid I don't understand your method.
Mosey

[steamer]

I think that is what he's saying Mosey....using the stock to support the work and cutting back in steps

Dave

[jerry kieffer]

Jerry,
The valve stems are to be 0.112" and .75" overall length, and .280" at the head.
Do I understand you to say that the size of the stock to be turned is large? Larger than the final size of .280?
And, you do not support the outboard end of the valve while machining, relying on a large diameter to keep it from flexing while turning??
I am afraid I don't understand your method.
Mosey

Mosey
         If I were turning valve`s utilizing your dimensions, I would start with slightly larger stock probably 5/16".   From that point, I would machine the stem in about three of four equal length steps.    In addition, I would avoid the use of any support such as a center.     While of no concern on larger items, tension on small work pieces from support can greatly effect accuracy especially if attempting small work on large machines.

Jerry Kieffer
 

[Mosey]

Got it, guys.
Thanks.
Mosey

[Lew Hartswick]

That technique works very well for turning taper pins.  (curtsey of Gail) I made quite a few brass shear
pins for the lathes at school using it. Started with 5/16 rod and turned about 2" with a taper of 1 : 50
small end about 1/8" (don't remember the taper pin no. ) Turn the entire reduction in one step. Works
like a charm.
   ...lew...

[Mosey]

Jerry and others:
What kind of finish do you get from turning the valve stems in the lathe?
I tried using a HSS cutter, sharp except for a small radius nose, honed to a polish, and I get a fairly smooth finish that is a very fine thread upon observation with a loop. On the other hand, if I use a Nikcole  Minisystem with Titanium Nitride coated insert the finish is shiny and smooth, much smoother than a ground cutter.
Then, do you polish the stem for final finish with Cratex or emory?
Mosey

[Steamer5]

Hi Mosey,
 Sounds like you are making progress. When you first posted I did a bit of googling, found that Tel had posted his version on" that other site". I didn't post then as I figured Tel would jump in......his latest hat fetish hasn't shown up so you might like to check it out.

Cheers Kerrin

[Mosey]

I will check out the Tel post, thanks.

I went back to kindergarten and resharpened my HSS cutting tool. Sharper rounded tip, diamond honed edge smoother. Did some test cuts at finest feed and highest RPM, and the curl coming off the work is a tiny wire like curl. About as good as it gets.
I think I'll go with it and plan on polishing the stem where it slides in the guide.
I plan on turning the stem down to about 0.001" over and polishing away the final thousandth.

I can't repeat the mirror finish from the Nikcole insert, must have burnished from rubbing, not cutting. Sure was pretty.
Mosey

[Brian Rupnow]

Mosey--I have turned many valves, down to as small as .093". Always start with stock slightly larger than the largest diameter of the valve head.   Let the "stickout" from the face of the chuck be about 3/16" greater than the total valve length from the face of the chuck. Turn the full length sticking out to the maximum diameter of the valve head. Start at the end farthest from the chuck and turn about 1/3 of the valve length to .002 or .003" greater than the finished valve stem diameter. Make note of the setting on your cross feed dial when you reach this point. Then move in and repeat for the next third of the valve length. Then move in once more and finish the stem length and then swing the compound for a finish cut at 45 degrees (you will actually be feeding from the backside of the lathe when you do this.) Every time I have tried to turn the valve to finished size I always end up going undersize and ruining the job. Have your valve guide finished and reamed to size first. Then do the 280 grit carborundum paper trick and hold a 1" wide strip over the  shank of the revolving valve stem at about 550 rpm and slide it back and forth on the revolving stem. Count 20 trips back and forth over the revolving stem and then try for fit in the valve guide. My personal experience is that about 20 trips back and forth on a cold rolled valve stem will remove about .001" of diameter, but that is a subjective thing. Once you get a nice sliding fit into the guide, do NOT cut the valve off from the parent material. Remove it from the chuck and cut the parent material about 2 1/2" back from the head of the valve. This gives you handle to hang onto for lapping the valve into the seat. after the lapping is completed, then set it back up in the lathe and use a parting tool to cut the valve away from the parent stock.--Or---If you have parting off issues, cut it off about 1/16" longer than is needed with a saw, then grip the stem in the lathe chuck and face the head down to the right length.---Brian