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How to find exact hight on a lathe

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Rcdizy

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#1
I have a quick change tool post on my King brand 14x40 lathe.

I recently bought a MT3 tool holder so I can drill from the tool post. I am looking forward to trying this because I can use the DRO for exact drilling depth, and clear chips easier and "Bird peck" easier on deeper holes. So nI hope this works.

Finding the centre from front to back wont be a problem because I can use the cross slide DRO to find centre.

How can I accurately find the exact up/down centre so I can set and forget the hight on the MT3 toolholder?
 

Jimsehr

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#2
Search One way to find center.
 

Superburban

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#3
If you don't have one, get an MT3 center. and a straight center. Put the straight center in the 3 jaw, and the MT3 in the holder. then just adjust the two points to match each other.

I guess you could also start a hole with the tail styock, then with a drill in the MT3 holder, align it to the hole.
 

Tozguy

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#4
As I understand it there will be a drill chuck on the MT3 arbor in the QCTP.
I would chuck up a short dowel pin in the spindle chuck and another dowel pin of the same diameter in the drill chuck.
Line them up on the same axis using a straight edge over both pins until there is no daylight showing.
Repeat to confirm by switching the dowel pins from one chuck to the other. Bear in mind that the lack of repeatability of the spindle chuck and drill chuck might require that you average out several readings.
 
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P. Waller

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#5
This will turn out to be a thorny question here I suspect.

I do this often on CNC lathes with QCTP's, I loathe these in every possible way. The way that works for me is sure to be incorrect but I will tell you anyway.

Place an indicator in the lathe spindle and spin it around the tool and adjust the tool post accordingly.
This will get you in the ballpark but not where you want to be, QCTP's are not terribly accurate when used this way. Then spot drill a piece of scrap from the tail stock, mount the drill and run it into the spot by hand and observe visually how far from center the drill point is, the movement will be obvious. Adjust it until it stops moving from center.
Drill hundreds of holes and call it a day.
 

Tozguy

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#6
Once the tool holder is on height you will need a way to align the axis of the drill chuck parallel to the axis of the spindle.
 
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P. Waller

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#7

benmychree

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#9
You know how to find center on the in and out direction, it is just the same process on the vertical centering, just "cut and try", or rather peck and try, adjust the tool vertically until it is centered, as proved by drilling a hole the diameter off the center drill's pilot, this is the same way as commonly used to center the tool on the cross feed axis. Folks try to overly complicate this task, it is quite simple. There is no need to indicate anything.
 

westerner

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#10
Joe Pie has a great video on setting lathe tool height. Not specifically on setting a drill in a QCTP, but the concept he shows will help, I believe.
Dhttps://www.youtube.com/watch?v=1MrjnIcscxI Darn sure took the quesswork out for me, and when the lightbulb lit, I had to grab my shades:big grin:
If the link won't work for ya, because I am a total noob at MANY things, just go to Joe Pieczynski, and look for the "Lathe tool height" video. He has helped me a whole bunch, just because he is a natural born problem solver, and just happens to run a very successful machine shop:cool 2:
 

Briney Eye

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#11
Joe Pie has a great video on setting lathe tool height. Not specifically on setting a drill in a QCTP, but the concept he shows will help, I believe.
Dhttps://www.youtube.com/watch?v=1MrjnIcscxI Darn sure took the quesswork out for me, and when the lightbulb lit, I had to grab my shades:big grin:
If the link won't work for ya, because I am a total noob at MANY things, just go to Joe Pieczynski, and look for the "Lathe tool height" video. He has helped me a whole bunch, just because he is a natural born problem solver, and just happens to run a very successful machine shop:cool 2:
+1 I watched Joe's video and immediately went out to the shop and used it to make myself a height setting tool that sits on the flat part of the bed way. Very handy.
 

T Bredehoft

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#12
Swinging an indicator (in the chuck) will not give you center. The indicator will read differently when upside down.
 

Cadillac

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#13
I would think indicating would be the most accurate but others have said different. Can someone explain how aligning by eye would be more accurate. I understand indicator sag but I would think it’s more accurate than by eye and feel?
 

homebrewed

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#14
I put together a QCTP-mounted drill chuck for much the same reason(s). I got a drill chuck with a straight 1/2" threaded hole on the back so I could use my 1/2" boring bar holder.

To line it up I faced two lengths of 1/2" drill rod and put one in the headstock chuck and the other in the drill chuck. Adjustment is an iterative approach. To start, I back the cross slide out until I can place the two rods next to each other. Then rotate the QCTP until the two rods are parallel, and lock it down. Then move the cross slide and carriage so the nicely-turned ends face each other and adjust the cross slide and tool holder height until you can't feel any step on the sides or top/bottom of the rods. A straight edge would work too.

I also made a cross slide lock so it wouldn't move around while I was drilling.

The arrangement is pretty handy if I'm step drilling -- the length variation in drills as I go from small diameter to large can exceed the range of my tailstock quill so I have to relocate the tailstock partway through the procedure. By comparison, the "quill" of my carriage-mounted chuck is the lathe bed so that problem is eliminated.

I did have to improve the fit between my carriage and bed (the lathe is an old 7x12). The carriage was tipping backwards due to the direction of the drilling force. Also, enlarging holes in brass using unmodified drill bits was far too "exciting" -- the drill would rapidly self-feed as the brass grabbed the drill. I dubbed a set of bits to get around that problem.
 
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petertha

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#15
I have the same brand/size lathe '97 vintage. I've eyed MT tool holders but don't have one. Does it have tang retention like what is in the tail stock if for example you inserted a large diameter drill with MT shank? Otherwise how does it prevent rotation, just socket friction?

I don't see establishing up/down and in/out center that big a deal because its essentially a point. But I am more curious about how you would ensure the MT axis is exactly aligned with spindle. Even if you rotated a DTI held in the chuck about the crest of an MT center, you would be tricked if the tool was off at an angle. maybe an alternative is insert an MT3-straight shank test bar & indicate at 2 different positions down the length? I bought one like this off Ebay. It was a made in India special but I was actually very pleased with its accuracy for the price.
Let us know how you get on. And some pics of it in operations would be nice.
 

Tozguy

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#16
Another way to align the drill chuck is to use a long drill bit and run it all the way into the chuck to see if the bit remains centered in the chuck.
This picture shows the set up although here the drill is too large to enter the jaws in the chuck as shown.
This is eyeballing it but you can get it quite well aligned if you use a test rod instead of a drill bit and chuck up a bushing that barely clears the test rod.
 

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Chipper5783

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#17
There seems to be way too much brain power going into this question. Anything over 1/2" I usually drill from the tool post (small drills from the tailstock). Drilling is a roughing operation - even if you had that aligned perfectly and exactly on center - you still would not get a very precise hole.

I have a CXA size PhaseII QCTP. I set the holder height once (using a small pointed piece of rod), I align the holder/drill with the axis of the lathe just eye ball. To set the horizontal position, I set the drill bit with the cutting edge sort of horizontal and just eyeball to get close enough to center (intent is to have two nice chip curls). It works great, very quick to set up, quick to clear chips.

Drill away.
 

P. Waller

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#18
Swinging an indicator (in the chuck) will not give you center. The indicator will read differently when upside down.
This only happens when you are wearing green shoes.
 

T Bredehoft

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#19
when you are wearing green shoes.
I must have been then. I secured a Starret Last Work on the end of a shaft against a pin in the end of the shaft. (Special job, just to check this problem) The Last work had been pointing down. I rotated the shaft 180º, the Last Word, (not really the Most Critical test indicator) moved .008. Gravity affected the insides of the indicator.
 

eastokie

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#20
wow its absolutely unreal all the different ways and added complication and made up tooling and even stands ???!!!!! ,,to find the "center" for lathe turning.. when i went through my 2 year vo-tech school,it took all of 20 seconds for the instructor to show us how to do it, he had a piece of round bar stock already in a 3 jaw chuck ready to cut, he moved the cutting tool close to the bar and then pulled out his 6 inch scale and put it between the 2 and cranked the cross slide so that there was just enough preasure to hold the scale against the bar, if top of scale was tilted back just a little then tool was just under center, exactly where u want it, no need to try and get cutting tool perfectly centered, just under center is good,dont over complicate things, it wasts too much time,, for internal boring u need the tool to be above center, just the opposite."Perfectly On Center" !!!! ????? what for??? it gets u nothing and wastes time..just below center makes sure that only the cutting edge is touching the work, the area below the cutting edge CANNOT be touching the work it will rub, and thats not cutting..sometimes when internal boring u have to raise the tool way above center to keep area under cutting edge from contacting work,,..people KISS ,setup time can be a real time waster..
 

Nobby

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#21
as newbie I found this tool very easy to use for cutting tools, as skill level increases will make a joe gauge. for tail stock chuck centering removed chuck and used two dead centers one in tail stock other in head bore then used small six inch steel ruler pinched between dead center

http://www.edgetechnologyproducts.com/pro-lathe-gage/
 

westerner

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#22
small six inch steel ruler pinched between dead center
I think this method will get most of us as close as we need to be! :encourage:
 

mikey

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#23
I've seen many, many discussions about the importance of getting a lathe tool/parting tools on center height. True to form, some think its important, others don't. My suggestion is to test it yourself and find out.

I don't like to guess and I don't rely on opinions so I did exactly that and found that going above center causes rubbing and deflection, while going below center increases wear and chatter. Getting on center seems to be the sweet spot where the tool cuts most accurately and finishes best. That led me to make a height setting tool over 30 years ago and I use one frequently.

This works for me but I know of at least one guy on this forum who uses his tool below center and seems to like it best that way, so test it and find what works best for you and go with that.
 

Tozguy

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#24
I recently bought a MT3 tool holder so I can drill from the tool post. How can I accurately find the exact up/down centre so I can set and forget the hight on the MT3 toolholder?
Just wondering why you want to dedicate an MT3 tool holder to drilling. I have nothing against it, I have dedicated a tool holder for drilling too but it was not being used for anything else. As a hobbyist much of my time is spent experimenting with set ups and trying different procedures just for the exercise. And my boss is OK with that.
 
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eastokie

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#25
ok here's one tool i will admit to making, and it does come in handy for other things too.i call it an alignment bar,,take a ft long piece of CRS , nice and straight and clean, about 3/4 od, put in 4 jaw chuck , indicate to .000 ,face off, take center drill in tail stock and drill, then FYI put a indicator on that 60 angle, and bet most of u reading this will get .001-.003 runout !! get a piece of HSS grind to shape, and use it to slightly recut the 60 angle, so u have no runout..remove bar, flip around and do other end also..put dead center in headstock,indicate to .000 and another center in MT3 toolpost,after u indicate toolpost holder exactly 90 degrees to ways,put bar between centers,and use indicator with magnet OFF, on the ways across the top of bar,,from headstock to tool holder,then u can raise or lower tool holder till its perfectly on center..this alignment bar can be used to get tailstock prefectly centered ,and also offset for cutting tapers..and as to "set and forget" your tool holder ,dream on !! our home use lathes are not ridged and straight enough,,u may have it perfectly centered at the headstock , and find it .003 low at the end of your ways.best to get it centered in the middle and call it done..good luck..
 

Dabbler

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#26
great idea, eastokie!
 

Dabbler

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#27
I have to partially disagree with a comment made above. Like all things machining, the context and the equipment you use will cause differing results!

I ran out and tested the \the indicator in the chuck thing... again. I also phoned a friend that has a 'perfectly' centred tailstock. and he used his Mitutoyo indicator and verified my results (to eliminate operator error)...

Using my Mitutoyo tenths indicator, with the sliding dovetails, using the larger spigot (looks to be 9mm, I forgot to mic it) I get no detectable sag. I won't vouch for your setup but by holding the spigot in the 3 jaw chuck, I can indicate my tailstock and on vert and horizontal readings it is exactly the same. the only variance is slight twitch from the surface, but that is barely detectable.

I know this has become a mantra here lately but it isn't always true.
 
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