What method do you use to find center height for your lathe bit?

What method do you use to find center height for your lathe bit?

I've made jigs and tried lots of different methods over time, but I still find facing off a bit of 40mm aluminium the easiest and I also find this method seems to give the best surface finish for me.

I use a digital height gauge to measure the height, and very carefully set it to 3.5" for my Super 7, using Dickson tool holders. This is because I want each tool to be at the same height so my tool offset tables work consistently.

I always do the same but use a 20mm brass bar instead. I use this method for both inside and outside tools. In my opinion this is the quickest method.

Jan

Like John, a digital height gauge.

I measured the height from both the bed and the cross-slide, and put a sticker on the headstock so I can't forget. Now, on the rare occasions I use a new tool I can get it set to centre height within seconds. Same applies if I need to scribe across a turned face.

Edited By Nicholas Wheeler 1 on 27/06/2019 07:19:36

I use a 6 inch rule and trap it lightly between the tool and a piece of round metal in the chuck and when it is vertical to the bed it is on centre height, quick and easy works all the time.

David

20-odd years ago I made George Thomas’ centre height gauge. Very nice design which can be used from the bed or the top of the cross slide. I use it all the time and can highly recommend it.

Facing is the final check, but I don’t understand the importance of using 40mm aluminium - seems to me to be a waste of time, effort and material! That is a waste of 75% of material cf a 20mm piece! Half the cutting time with 20mm with exactly the same result. Less diameter than that would suffice, of course.

But possibly a waste of time if surface cutting something of large diameter in tougher material with a heavy feed while using a less than perfectly rigid set up, when an extended cutter in a large overhang tool holder on a less than perfectly rigid lathe will alter that setting anyway. Reports of difficulties with parting off makes that perfectly clear to anyone who thinks about it.

+1 for bar (mine is aluminium), but I also test by eye against a centre in the tailstock. Main problem with that is getting the right part of my varifocals in the view!

Iain

Ditto, this method also works horizontally for drilling bar stock in a drill press / milling machine.

+1 for the six inch rule method. That was how I was taught as an apprentice.
Quick and no material waste.

Who said it was important except yourself?

It's actually 39mm and I have 6 x 3m lengths of the stuff that a friend liberated and gave to me from a place that he worked at that closed down.

Your posts are always such a pleasure and a real treat to read, please keep up the effort.

Mostly I just eyeball it. It really is not that critical. I know that a piece of 3/8" HSS is dead on height. If I look at the end of the tool and see it has been ground down by 20 thou or so, by eye, I slip a piece of half-millimetre sheet steel under it. I keep a stack of these shims on hand. For 1/4" bits I have some 1/8" shims made up to bring them up to height. Half mil. shims are then added to this as needed to make up for tool wear/sharpening. Always erring on the side of setting the tool bit a bit low if anything, as this gives a better result than too high. In fact, setting a bit low usually gives a better result than being dead on centre height.

Or I will use the steel ruler method if I need to be precise for some reason, like parting off. I also have something like the GHT height gauge made from the exhaust valve of an old Harley with a point from an old trammel clamped on at the right position. But very rarely use it.

Edited By Hopper on 27/06/2019 08:20:37

I made the Hemingway centre height gauge but also found an industrial one at a local tool supplier, better than the Hemingway as it has a double ended point, one end face up to set to the centre in the tailstock and the other face down to set the tool to.

I'll take a snap of it.

Mick

I like to keep things simple.

I use one of these straight shank dead centres in whichever chuck I am using:

**LINK**

+ another one. Simple, no faffing.

Not often necessary - I have a milled packing insert for my 4-way toolpost that's already the correct height for a 1/4" square HSS blank, so I only need to do additional height setting if I've had to grind the top face down for whatever reason. I avoid doing that if I can.

I use a centre in the tailstock to get close then take a facing cut off the end of a piece of scrap bar , i have one of the edge technology height setting tools though i rarely use it but if i had to set up a lot of tool holders it would be a handy tool.but i would have to set up the 3 jaw to use it or stuff around getting the locating shaft running true in the 4 jaw i mostly use .

The upright rule certainly works, as does facing till you get no centre pip. I used both methods successfully for many years - and still do so occasionally when it's convenient/quick to do so.

But the rule method doesn't always work for some set-ups and if you change or move the tool mid-operation (break the tip on your diamond toolholder bit for instance) - you can't always just machine a pip mid-operation and of course neither work well for setting up boring bars...

So, what I (finally) did for both my lathes was to just turn a piece of scrap stock true (can be anything, any diameter) and with it still in the chuck/collet - measured its top-height from both the bed, cross-slide and top-slides using a Vernier height gauge. Subtracting half the turned diameter from these measurements gives you the key centre height references for your lathe and enables you to set-up simple height setting gauges and other work-holding devices very simply. You only need do it once and note the results for future use...

Regards,

IanT

Edited By IanT on 27/06/2019 09:07:12

Usually just scratch a line on the end of a random bar with a tool of known height and then set the new one to that, I find the fine line produced crisper than a ctr which never go to an exact point. Then a test cut if the tool is suitable to take facing cuts.

May use the ruler with HSS but not keen on doing it with insert tips due to risk of crumbling the edge particularly **GT ones..

If all else fails I know the exact height from cross slide to ctr and can set a height gauge to that

The obsession with centre height was just invented to intimidate apprentices. Rarely matters until you are turning clock arbors. When wanting to face without a pip the OP's method effectively works but on the job itself to save time.

The 'Southbend/Boxford 'Know your lathe' book actually recommends setting above centre height for the reason that is so obvious it doesn't explain it (but I have in previous threads on this topic).

I simply eyeball the tool tip against a centre in the tailstock. If i need to face off the workpiece I might tweak the tool height to remove any centre pip.

Andrew