Thread: Cylindrical Square

Ray, assume the base has a 10 degree "tilt" and the taper is 5 degrees. Put the indicator on the cylinder and rotate it to the maximim reading on the dti. At that point the surface contacting the dti will be sloping toward the dti minus 5 degrees (with reference to the plate it's standing on). Now rotate the cylinder as you described until the dti reads the minimum reading, the cylinder will be sloping away from the dti at the point of contact 15 degrees. Find the mid point as you described in your note. That point will be sloping away from the dti at 5 degrees, ie the amount of taper only. If the cylinder has no taper (as measured with a micrometer etc) then at that point (and assuming the cylinder is perfectly round, so will its mate diametrically opposite), the cylinder surface will be perpendicular to the surface it's standing on. If it has a taper it will be the taper angle.

Pete

Hi Pete,

Yes, I see your point. In general, with a non-tapered tilted cylinder the edge will swing above and below 90 degrees equal amounts, when the cylinder is tapered, the 90 degree point moves towards the point of maximal tilt as the amount of taper increases, in the limiting case the 90 degree point is also the point of maximal tilt.

Regards
Ray

PS I've discovered you can actually buy specially tilted cylindrical squares, that are marked around the circumference for calibrating squares.

This book calls them "Direct Reading Cylindrical Squares"

Originally Posted by RayG

Hi Pete,

Yes, I see your point. In general, with a non-tapered tilted cylinder the edge will swing above and below 90 degrees equal amounts ...

Precisely. That's why you first need to determine that the cylinder has no taper. However that's very easy to do by simply using a micrometer, although there are other methods that are arguably more accurate, I think it's accurate enough for home shop purposes. Once that's done, then use your method to determine the point that's perpendicular. The only thing I've suggested in the past however is to locate the cylinder in some form of V. If held against a flat surface no matter how hard you try not to shift it along that surface as you rotate it, this is pretty fine work we're talking about, and it will fractionally move. Then you're faced with sliding the cylinder up and down slightly to confirm the maximum and minimim points ... a PIA I reckon I'd rather avoid.

Yes I've heard about those squares, but to be honest I've never seen one. Speaking of which, I'm trying to buy some things from the company you bought yours from, they better go nameless as it feels like trying to pull teeth! They're not exactly helping me with the buying process!! In the end I decided to go for a granite square instead of the cylindrical one.

Pete

Hi Pete,

This is a repeat of what I posted earlier in this thread, you must have missed it. The notch is just visible at the base of the cylinder. Also you can see the relevant marks on the top of the cylinder.





Rotating against a 0.001mm indicator to find the high and low spots, and watching how the needle moves to see that there are no bumps or dips, I found that it was pretty well essential that the indicator be mounted on a base that registered against the cylinder, there is a notch that locates the cylinder. Dust is a major menace, but with a little patience and care you can find the highs and lows.

...........................................................

Regards
Ray

Thanks Ray, I'd seen that photo but hadn't noticed the notch until you pointed it out. I was just going off of the pdf notes you posted. Dust is amazing isn't it, it seems like surface plates have an inbuilt dust magnet and things you would even notice suddenly feel as if you're working in a gravel pit!

Pete

Make a small cylindrical square last night/yesterday afternoon..

Have not checked it for squareness yet but it should be not too bad...

Some pictures showing it.... I drilled a hole full length through it and tapped 8mm both ends... The photo showing the micrometers is from either end... But take the measurement with a grain of salt, as once you get into those sorts of dimensions it gets very hard to measure consistently... Measured it up and the needle says 0.0001" taper total error... So I shall now go and gloat on HSM how my workshop grade lathe is good for 50 millionth's squareness and that paying extra for the likes of a Monarch 10EE is wasted money...

Hi RC,
It certainly looks good. Is that straight off the tool or was there some lapping done?

I almost asked what diameter bar you used
About 100mm long?


What was the rule again "no more than 2.5 times dia"?

Stuart

Originally Posted by .RC.

Measured it up and the needle says 0.0001" taper total error...

Hi .RC,

2 micron taper error, not too shabby, who needs a cylindrical grinder..

Even if the base isn't square with the sides, there should be at least 2 points on the diameter where it is exactly square. I'm interested to see how goes when you rotate it.

What's the accuracy of that Tesa level square like?

Regards
Ray

Hi Richard

Is there a reason your centre is in the 3 jaw and not in the headstock spindle? Also did you have to do any adjustments to the tailstock to get that kind of accuracy? Just want to know for when I give one a go.

Phil

I put it in the three jaw and turned the centre from there as it takes out one more variable (the centre) in the process..

Reading old turning books, when turning between centres and using a centre in the headstock the first part after installing the centre was to turn/grind it to true it up...I did not wish to do that to one of my centres...

Originally Posted by .RC.

I put it in the three jaw and turned the centre from there as it takes out one more variable (the centre) in the process..

Reading old turning books, when turning between centres and using a centre in the headstock the first part after installing the centre was to turn/grind it to true it up...I did not wish to do that to one of my centres...

Richard, can you run that one past me again, I didn't follow that. By "it", did you mean you turned up a new centre by simply chucking some stock in the 3 jaw and turning a taper on it? That would certainly make sense if you did and what you said you were trying to achieve. FWIW I have found all my cheapie Chinese centres have been accurate as received, but I guess like a lot of Chinese stuff that would be purely the luck of the draw. My new lathe is unfortunately MT4 taper (well actually that's obviously good, but needs much new tooling), so I guess I get to play lotto all over again. I'll try an MT4-MT3 adaptor, to get me out of strife, but don't see that as a good long term solution where real accuracy is required.

Nice job on the square by the way. I'll also turn one on the new lathe as part of checking its accuracy once it's installed and levelled.

Pete

Originally Posted by Pete F

Richard, can you run that one past me again, I didn't follow that. By "it", did you mean you turned up a new centre by simply chucking some stock in the 3 jaw and turning a taper on it? That would certainly make sense if you did and what you said you were trying to achieve. FWIW I have found all my cheapie Chinese centres have been accurate as received, but I guess like a lot of Chinese stuff that would be purely the luck of the draw. My new lathe is unfortunately MT4 taper (well actually that's obviously good, but needs much new tooling), so I guess I get to play lotto all over again. I'll try an MT4-MT3 adaptor, to get me out of strife, but don't see that as a good long term solution where real accuracy is required.

Nice job on the square by the way. I'll also turn one on the new lathe as part of checking its accuracy once it's installed and levelled.

Pete

Pete
Please lets know when the Lathe is installed, I would like to visit & meet up with you.'
Just a short run through the Gorge.
I realise you have been travelling, so whenever you are ready.
regards
Bruce

Oh yes sorry Bruce, things have been just stupidly busy lately. Thank goodness for Skype video or my kids would forget what I looked like, the dog already seems uncertain when I get home each time!

I will also put up a thread or two on the adventures of the lathe. Without getting this thread OT, it's a brand new Hercus 260, a bit "shop soiled" but otherwise hasn't ever turned metal and is still covered in cosmoline. Perhaps that in itself is of interest to a few members in the Hercus section. The other thing I'll put up is the precise procedure I went through re-importing it back from Hong Kong to home for those considering importing machines directly. It all went extremely smoothly until it hit Oz. As I said to GregQ, $730 to crate and ship from dealer in Hong Kong, a 1/4 way around the world to the docks in Sydney. To get it another 100 m from the wharf to the back of my ute cost me around another $1K, so I wasn't impressed with that! The full story when I get a chance to sit down and add up the total charges.

Pete

Originally Posted by Pete F

Oh yes sorry Bruce, things have been just stupidly busy lately. Thank goodness for Skype video or my kids would forget what I looked like, the dog already seems uncertain when I get home each time!

I will also put up a thread or two on the adventures of the lathe. Without getting this thread OT, it's a brand new Hercus 260, a bit "shop soiled" but otherwise hasn't ever turned metal and is still covered in cosmoline. Perhaps that in itself is of interest to a few members in the Hercus section. The other thing I'll put up is the precise procedure I went through re-importing it back from Hong Kong to home for those considering importing machines directly. It all went extremely smoothly until it hit Oz. As I said to GregQ, $730 to crate and ship from dealer in Hong Kong, a 1/4 way around the world to the docks in Sydney. To get it another 100 m from the wharf to the back of my ute cost me around another $1K, so I wasn't impressed with that! The full story when I get a chance to sit down and add up the total charges.

Pete

I can't say I'm surprised by the local charges. It's all a mystery but you pay for it.

WRT centres in the 3 jaw, all you do is chuck up a piece of round stock, preferably with a shoulder so it can't slip backwards, then do a skim cut on it to get the point running true. No need for it to be hardened or whatever as it rotates with the workpiece, you just want the point concentric to within the limits of the lathe. Doing it like this is easy and it doesn't matter how far out (within reason) the 3 jaw is, because you don't remove the centre until you've finished.

I've got a reducing bush & hard centre for my Chipmaster but I've never used them in the entire time I've owned that lathe.

Did you get that pic of my Emco Maximat 11 I sent?

PDW