Thread: Making a Cylindrical Square.

Originally Posted by OxxAndBert

I just had a look at the linear shafting spec on statewide bearings website.
60mm linear shaft is HRC60-64, and diameter tolerance is +0/-19uM (0.00075")
Not saying all linear shafting is made to those specs, but I'm guessing decent quality ones likely are.

Steve

Apologies Steve, I know that you wrote linear shafting, but I saw line shafting, different specs altogether. While 19 microns is a bit higher than you would want, it is the worst case scenario, and if you are lucky, your piece might be much closer, and for that matter, for home shop use 19 microns would normally be much tighter than almost every measurement that we make.

With a bit of care and a well sharpened hss cutter, most people would be able to turn a shaft more parallel than 19um taper.

Further, the issue of the perpendicular can also be taken care of while it's still in the chuck.

No need for a gudgen pin.

Simon

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The advantage of a piston pin is that they are already hardened, anything soft will bruise/burr easily.

Yea i get that but with those tolerances and the fact that you still have to deal with squaring the ends makes it difficult.

How do you plan on improving it's parallelism and how do you plan on squaring one end and relieving the inside?

Simon



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I will be honing the inside to improve it a little then putting it on a mandrel and grinding the outside and ends without removing it from the mandrel until it is finished. That is similar to the way I did this one at RMIT during my apprenticeship.

Cylindrical Square.JPG

I see. That counts me out, I don't have a cylindrical grinder!

Still, i'm keen to see the results.

Simon



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Originally Posted by simonl

Also, parallel sides are one aspect but how do you intend to square the end to the required tolerance?

I'm interested because I've been keen to make one too.

Simon

It's a basic working between centres task - first the lathe to take it roughly to size (heat treat?) and then a cylindrical grinder to finish. Once the diameter is parallel, the usual trick is to dress the side of the grinding wheel on your cylindrical grinder so that it will grind the ends.

For a home workshop situation, turning one from alloy steel or cast is an option. Your lathe has to be able to turn straight and parallel (rules most of us out I guess), but after the diameter is done, the end is faced. Because this is done between centres and most of the ends are recessed, effectively the facing operation produces a contact surface that will automatically (due to the generating process), perpendicular to the axis.

Michael

Not sure if this is an appropriate place to suggest this (mods please move/delete if it isn't), but I had a bit of a look around today and looks like we could get 250mm long pieces of 60mm linear shafting for around $50 each. Probably needs 4+ people to make it work out.
If there's any interest in that let me know.

Steve

Originally Posted by Techo1

I will be honing the inside to improve it a little then putting it on a mandrel and grinding the outside and ends without removing it from the mandrel until it is finished. That is similar to the way I did this one at RMIT during my apprenticeship.

Cylindrical Square.JPG

G/day Techo, is the threaded hole for a drive pin

steve you can get chrome bar that has been hardened and tempered.
I have no idea how good or bad linear rail is to grind but i do know that if it is not tempered (stress relieved) properly that even
a small change in temperature will move it one way or the other, not only while grinding but also environmental temp swings
have the potential for the cylinder to bow. It might only be 1 or 2/10ths but you are trying to make a precision instrument and
I think that you want to be sure that the material is stable, I say potential to bow because you dont really know what stresses are in the material and stress relieved material is much more stable when machining it. It is surprising how quickly a non stress relieved shaft will bow with "only a tiny iddy biddy little bit of heat" if you are grinding it without coolant.

Here are a couple of options,

• 4140 Chrome Bar
  
  • W-Nr 1.7225, AS 4140, BS EN19A, AISI 4140
  • Low alloy general purpose high tensile hardened and tempered steel. Ideal material for highly stressed component applications.
  • Size Range Rd 19.05mm - 101.6mm, Induction Hardened Rd 25.4mm - 95.25mm
  
  
• 1045 Chrome Bar
  
  • EN No (W-Nr) 1.1191/1.0501, AISI 1045, JIS S45C, UNS G1043
  • Fully-killed medium carbon steel. The traditional product used in the manufacture of hard chrome bar.
  • Size Range Rd 12mm - 171.45mm, Induction Hardened Rd 25.4mm - 127mm
  
  

https://www.buau.com.au/chrome-bar.php

cheers, shed

Originally Posted by shedhappens

steve you can get chrome bar that has been hardened and tempered.

I have found it's dimensions to be quite ordinary. It is suitable for what it is designed to do, but even along short lengths expect a variation on diameter of 0.0254mm

Originally Posted by shedhappens

G/day Techo, is the threaded hole for a drive pin

Yes Shed, there is a 6mm taped hole in each end to drive it between dead centers.

Originally Posted by .RC.

I have found it's dimensions to be quite ordinary. It is suitable for what it is designed to do, but even along short lengths expect a variation on diameter of 0.0254mm

Yes RC, that material is not good enough dimensionaly as it comes for the intended use, here are the specs https://www.voestalpine.com/highperf...Chrome-bar.pdf
I was more concerned about the stability of the linear rail, I dont think that it is quality stuff and I would not like to go to
the effort of making a precision cylindrical square with it only to find that it wiggles around with temperature change later on.

Originally Posted by OxxAndBert

had a bit of a look around today and looks like we could get 250mm long pieces of 60mm linear shafting for around $50 each. Probably needs 4+ people to make it work out.
If there's any interest in that let me know.
Steve

steve it is probably a bit premature at the mo as I have not made sparks with my grinder yet so I cannot say how accurate it is
going to be, I should know by the weekend. The chrome bar should only need a whisker taken off to true it.
All going well with the grinder and if you can get a few punters on board we could do a production run of these cylinders on the churchill and square the ends on the T&CG,
Bohler has a minimum order charge of $150.

cheers, shed

Hey if any of you people don't want help or advice or have a different ideas about how to do something or disagree with me about
anything i say... SPIT IT OUT..... i have my big boy pants on.

Right about now i feel as though i am looking at a bunch of autistic kids looking at their toes.......

what do all the people want to make one of these things for?
ive got 2 of them but have never used them.
aaron