# First chuck backplate turning/setup



## GunsOfNavarone (Feb 13, 2020)

So, my G0602z came with a 5" 3 jaw self centering and a 6 .5" independent 4 jaw. I do a lot of rod that is too big for the center hole of the 5" and I can kill 1 5-20 minutes indicating in on the 4 jaw so if course the best answer was to get a bigger self centering chuck. I just received my Shars 6" self centering 3 jaw. Here's my next challenge. It came with a backplate that is a 1.5" 8 tpi 
I don't think I will have room to turn that I to the needed 1.75" 8tpi the Grizzly uses, so I ordered a 6.5" plate from them. I really what rumours little as possible and the 2 things I 'm sure I will have to do is turn the register down from the 6.5" Sanou chuck they use to the 6" of the Shars . The lathe will take care of the centering of that so I'm not too worried but I've heard horror stories of turning cast iron. What inserts do I use for cast iron? (Not size shape etc...)
Also, the mounting screws for the chuck to the plate, any secrets to getting those dead on? I remember drilling my welding positioner backplate for its chuck, "dead on" was NOT my end result. I tbought I could run a scratch mark on the larger of the hole circumference  placement, but the 120° placement is another issue, but isn't the larger pretty damn close to being a dividing head??
I know you guys have some easier ideas, I'm very interested in hearing them!
Thanks guys


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## Cadillac (Feb 13, 2020)

If I was gonna do a backplate I would mount a 4jaw on the lathe probably have to flip the jaws. Center your part in the 4jaw off the existing register. I would then cut the threads and the register. For tooling I’d use hss or a positive carbide insert that is sharp. Once the threads and register are cut I’d remove the 4jaw and mount the new backing plate. Once mounted I’d cut the register for the chuck. For the boltholes to mount chuck the easiest would be a rotary table. If you don’t have one and the holes go through the chuck then use transfer punch after the register is cut. Without through holes or rotary table you gonna have to go by cordinants on x&y. Or a index plate on your lathe spindle and a live drill setup on the compound. Good luck.


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## GunsOfNavarone (Feb 13, 2020)

The plate i orders from Grizz will fit into my spindle, so I'll go straight to register cutting. It sounds like I don't need and special carbide inserts for cast iron? Most of mine are pretty basic...maybe TiN coated. I do have a indexing head, but I feel like there is some trick to indexing the lathe, but now that I think I about it, other than finding the 120° spacing positions, there would be no way to drill those holes. I just know there is about ZERO room for error so I'd like to one and done this and my confidence is somewhat low, mostly as I have never done this material or operation before.


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## benmychree (Feb 13, 2020)

For the holes you can use transfer screws, screw them into the tapped holes in the chuck with the points sticking above the machined surface, insert the backplate into the recess and whack it with a soft hammer where the screws are, it gives a nice sharp center punch mark to start a center or spotting drill.


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## GunsOfNavarone (Feb 13, 2020)

I guess I'm a bit limited on my knowledge of transfer screws. Being that my register is a 16th of an inch tall (maybe less) I don't know if the transfer screws will allow it to fully engage the register (and be settled dead on center) before the hit the back plate?


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## benmychree (Feb 13, 2020)

GunsOfNavarone said:


> I guess I'm a bit limited on my knowledge of transfer screws. Being that my register is a 16th of an inch tall (maybe less) I don't know if the transfer screws will allow it to fully engage the register (and be settled dead on center) before the hit the back plate?


They will screw in to just barely flush, just enough to make a mark.


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## GunsOfNavarone (Feb 17, 2020)

So I just got the back plate from Grizzly. It will fit my lathe and I won't have to machine the threads. I only have about .009 to .010" to take off the receiver..I could probably tighten it down with the mounting bolts and get it to fit. So, what I need to do is;
take a light cut off the surface the chuck bolts down to and the LIGHTEST cut to the circumference of the receiver (if I'm able to take that light of a cut...  .0005 off??) Does that all sound right? The new chuck has 3 mounting bolts and this plate has 4 so  will have to drill tap new holes. I reaaly want to keep the runout to minimum, with that receiver being onsize..I don't know. Isn't already dead on center (the receiver?) Dead center of a rotating part is dead center? I KIND of understand the light surface cut off mounting leadge having some variable but not center of a rotating mass. (?)


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## DavidR8 (Feb 18, 2020)

By receiver do you mean the register that fits into the back of the chuck?


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## GunsOfNavarone (Feb 18, 2020)

Sorry, yes. Register. I fell asleep about 10 minutes after typing that...12 hour days killing me. I’m just perplexed that the register that is already cut into backplate, would be different if I did a light skim cut. Isn’t centered...centered?


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## rgray (Feb 18, 2020)

I think your best move would have been to practice and get better with the 4 jaw.
Takes me about 30 seconds to center something in the 4 jaw.
No it wasn't that easy from the start but getting familiar with it and comfortable is not that hard.
Can't remember the last time I used my 3 jaw chuck.
I used it all the time when I first got my lathe and was learning, but now It just sits on the bench and it's either 4 jaw or 5c collets for me.


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## GunsOfNavarone (Feb 18, 2020)

I’ll get there with the 4 jaw, but why spend 20 minutes indicating in round bar...that seems like something better suited for a salt centering jaw. I purchased the back plate...2 of them if I’m honest, but one of them I need to open up from a 1” to a 1.75” and thread it, the other plate I just “need” to take a skim cut 
off off of...I’m just Thuringia to learn WHY?


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## Chipper5783 (Feb 18, 2020)

The bigger 3 jaw chuck will be handy.  You can make the transfer screws from a cut off bolt (for a "one off" it doesn't need to be hardened) - just cut off a bolt and point the end nicely using your existing lathe set up.  Then file two flats at the point so you can turn it with needle nose pliers (you only want it to stick up slightly).  You can do it one hole at a time: mark with transfer screw, center punch, drill, assemble with one bolt and mark the next.  To begin, you want to make the holes size on - but once you have all the holes, increase the size (i.e. 1/64 to 1/32" over to ease assembly).  Don't fuss too much about the positioning - it does not need to be within 0.001" - the bolts do not locate.

As rgray says - learn to use the 4 jaw chuck.  It is not a big deal and work really well.


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## DavidR8 (Feb 18, 2020)

GunsOfNavarone said:


> Sorry, yes. Register. I fell asleep about 10 minutes after typing that...12 hour days killing me. I’m just perplexed that the register that is already cut into backplate, would be different if I did a light skim cut. Isn’t centered...centered?



If the register on the backplate is .009 oversize I don’t think that it’s going to fit the chuck. 

I was in your situation a while back. New backplate for my 4-jaw. Didn’t want to mess it up. 

I took careful measurements of the register on the backplate and the corresponding hole in the chuck. 
I needed to remove about .005. 

I didn’t trust my metrology skills to just go by the numbers so I took it very slowly and after every cut I tried fitting the chuck until it went on. 

When I got the register right then I took a facing cut of the mating surfaces. 

I know that it’s a 4-jaw so any runout can be addressed but I still wanted it as good as I could manage. 


Sent from my iPhone using Tapatalk


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## GunsOfNavarone (Feb 18, 2020)

Can anyone answer that question? If for all intents/purposes, lets say the back plate is made perfect, same for the chuck. How does the skim cut on mating surfaces and the register cut (besides allowing the chuck to seat properly) adjust for my setup and the error inherent in the lathe? I'm trying to picture the spindle not being dead on parallel and how a skim cut on the actual lathe the chuck/plate will be used on will address this. Being it rotates, you can't make any cuts that can offset these issues. None of the answers will change my need, I'd just like to learn something here.


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## GunsOfNavarone (Feb 18, 2020)

Alright, went to turn the back plate. The perpendicular position....won't reach, parallel position...still an inch or more shy from reaching back plate. It seems against whats trying to be achieved if I mount the back plate in a chuck...no? The carriage
	

		
			
		

		
	



	

		
			
		

		
	
 is all the way in at this point.


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## Tozguy (Feb 18, 2020)

Why the skim cut....
The important reference point is the axis of rotation of your spindle. The axis of rotation is different from the center of mass by an unknown small amount. Also referred to as runout which in many cases is too small for us hobby types to measure. So the only way to get a back plate 'perfect' is to turn it on the spindle it will be used on.


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## mikey (Feb 18, 2020)

I have a few comments:

You now have a backplate that threads onto your spindle and you want to accurately mount a chuck to it. The plate has a female taper in the back of it that mates to the male register on the spindle, right? So, assuming those tapers fit well, you now you want to mount the chuck to the plate as accurately as possible. Your backplate is not yet machined and the snout in the center of the backplate has to be machined to fit the hole in the back of the chuck. Is this an accurate summary?
Assuming the above is accurate, what needs to happen next is to take a skim cut on the face of the backplate to true it to the spindle. In the pic above, you cannot even reach the backplate with your tool. I suggest you try turning your compound so it parallels the ways and put the tool holder on the side of the tool holder closest to the center of the lathe. If this is not enough to reach the back plate with your tool, extend the compound out a little bit and lock it down before taking cuts. If you still cannot reach it, you might try a boring bar.
The cut on the face of the backplate is just a light truing cut to make the face of the plate perpendicular to the spindle centerline. Take light cuts until the tool is able to face the entire surface, then back out. Now dial in a tiny bit more depth of cut, maybe 0.005", increase your speed and take a final finishing pass to achieve a nice surface.
The next step is to trim the center snout to fit the hole in the back of the chuck. Measure the hole and then measure the snout. There are two schools of thought on how to best do this. One contends that you should make this a light press fit, on the order of 0.0005 - 0.001" would do it. The other way is to make the snout about 0.002-0.003" smaller than the hole. This allows you to install the chuck and knock it into alignment before tightening the chuck mounting bolts. Samchully, maker of some of the best chucks in the world, suggests the latter approach. Our very own @darkzero has also done it this way and calls it the "tap-tru" method of chuck alignment. Other guys have done this by cutting too much off by mistake; they call it the tap-tru method, too, but don't mention the mistake part. Whichever way you go, try to do it on purpose and then just trim the snout to your desired size.
Then mount the chuck and mark the holes. If the screws pass through the chuck body, use transfer punches. If the screws pass through the plate from the back, take the plate of and use transfer punches from the back. 
Drill and tap and you're done.
Before you do any of this, I strongly suggest you plug up the spindle bore of your lathe with a rag or some other stuffing to prevent chips from getting into your spindle bore. These chips will eventually make it back to your gearing in back of the headstock and wear them down. I also suggest you cover the entire lathe with plastic painter's tarps or some other thing of your choice; leave only the backing plate and cutting tool exposed. When the job is done, brush any loose particles off the exposed surfaces onto the plastic and wipe those surfaces clean, then remove the plastic. Then clean the hell out of the lathe until there are no particles anywhere. Trust me; please do this.

See, not much to it, eh?


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## DavidR8 (Feb 18, 2020)

Yup, what @mikey said. 



Sent from my iPhone using Tapatalk


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## GunsOfNavarone (Feb 19, 2020)

Thanks guys & @mikey I will be sure to cover everything up. I said I would never turn cast iron..THOUGHT I’d never need to. My Kathe isn’t ridged enough to turn the compound perpendicular, but it’s just a skim cut..
I noticed the chuck has plugs in the backside (I assume for balance) this brings up the question, The new back plate is drilled  for 3 holes already, I need to clock it about 20 degrees & drill 3 more holes. The hole distribution (therefore balance) will be off. I could fill the old holes with lead or cut off bolts but the balance will no longer be “perfect”. Do I bother with this issue?


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## derf (Feb 19, 2020)

Why would the balance be off? The chuck is already balanced, and if the back plate is solid, it probably close enough. I'm assuming the original 3 holes are equally spaced, so put the other 3 holes between them.


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## mikey (Feb 19, 2020)

I agree; I wouldn't worry too much about the balance.


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## GunsOfNavarone (Feb 22, 2020)

Update. I skim cut the contact surface and lightly touched off the register. I used transfer screws and marked the plate and put the back plate on my indexing head in vertical position. Indicated in the part and found center of the punch marks...ran a spotting drill the a 6.5mm drill bit with 120 degree seperation and punched them through. My last step, either use a tap OR I have these spiral drill/taps to take it to 8mm x 1.25 tpm. I hate tapping though I normally do Stainless. Anyone ever use spiral drill taps? Not gonna lie, I'm a bit skeptical so I'm putting the last step off until tomorrow.


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## mmcmdl (Feb 22, 2020)

Spiral flute taps , spiral point taps . Spiral drill taps ? Are they a drill and tap combined ?


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## GunsOfNavarone (Feb 22, 2020)

@mmcmdl yes sir. Drill/tap and even chamfer.


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## mmcmdl (Feb 22, 2020)

Well , I've never !  I'll have to check them out , never seen one .


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## GunsOfNavarone (Feb 22, 2020)

Nevermind....I'm a knucklehead. The back plate doesn't need to be threaded..just gotta open the holes up another mm and give it a test. I did all I could, took my time. Its in Gods hands!
These are the type of drill/taps
Spiral drill taps


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## mmcmdl (Feb 22, 2020)

Designed to tap up to 10-gauge metal 

Not sure that would work even if you needed to tap those holes .


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## GunsOfNavarone (Feb 22, 2020)

Well, technically they are these...though they don't say how thick of metal they are for..there is a reason for my skepticism.
McMaster


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## mmcmdl (Feb 22, 2020)

Ok . They look like the smaller ones would work . I sure wouldn't trust a 1/4" hex to drive anything over a 1/4-20 tap though .  No way it would drive a 3/4" tap !


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## mikey (Feb 22, 2020)

Okay, so the chuck is mounted? Are you happy with the fit?


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## GunsOfNavarone (Feb 22, 2020)

Mikey! Mikey! These things take time... Actually I got called in for dinner, now were lounging around. I'll for sure open those holes up/mount it and check run out tomorrow. I sure am hopefully its very good, though I couldn't tell ya how the originals are that the lathe came with...that's just a bit ironic..no?


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## mikey (Feb 22, 2020)

Time, hell! You going to make us wait?   

Glad you got it worked out. First times are tough but you got it now.

EDIT: Forgot to add that lounging around with your wife is the best thing to do. I am sorry to hear about her challenges and will keep her in my prayers.


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## GunsOfNavarone (Feb 23, 2020)

@mikey thanks brother


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## GunsOfNavarone (Feb 23, 2020)

Looks like just under .002? I’m not sure where/how I measured is copacetic? I’m a .02” tolerance kinda guy...so well under that!


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## mikey (Feb 23, 2020)

Mike, measuring on the outside of a chuck gives you no useful information. What we want to know is how accurate the chuck is on the inside. You are dealing with a 3 jaw scroll chuck so to check how accurate it is you have to turn something in it and then check the run out on that thing. Here are a few things to ponder:

A scroll chuck should be dead on accurate for first operation work. That is, if you take a work piece and turn it for the first time and then check the run out on that piece, it should be zero. Even if the surface of that work piece is not perfect, the resulting turned surface should be concentric with the spindle centerline as long as you do not remove it from the chuck. This is called a first operation ... the first time something is turned.
If you wish to measure how accurate your chuck is, measure that piece you just turned in that first operation. Do not remove it or loosen the jaws once you turn it. Put a dial indicator in your tool post and bring it up close to the chuck. Get the tip of the DI on center and zero it. Mark the work with a Sharpie somewhere close to the tip of the DI, then manually make a single revolution of the chuck and realign the mark with the tip of the DI. The DI should return to zero. If so, make another revolution and watch for any movement of the needle. In a first op, there should be no significant movement; that is, it should read zero run out. If there is run out then you have a problem with the chuck jaws or some other part of the chuck. Keep in mind that you cannot evaluate a thing running under power like in your video, be it the chuck body, a spindle or a test bar in the chuck. You have to do it manually.
Now, if you took a test bar or pin or polished rod and mounted it in your scroll chuck and did the same run out check we just did above, that chuck will run out. On a high end chuck, this might be somewhere in the 0.001-0.003" range, and this will be true for any size of rod you put in there. On a lower end chuck, run out may be much higher. Does this tell you anything useful? Yup, it does. Putting something that has been previously been turned into a scroll chuck will always run out to some degree. If you turn something in a first operation, take it out of the chuck and then reinsert it in the chuck that work piece will have some degree of run out. Once you remove something done in a first op, the only way to get it to run concentrically with the spindle centerline is to put it in a 4 jaw independent chuck and dial it in. So, for first op work, use the scroll chuck. For second op work, use the 4 jaw or a collet chuck.
If you want to know how much run out your chuck really has, chuck up an accurate pin or end mill and measure it like we did in bullet 1. That will give you the run out for THAT pin. Now, if you take another pin of a different diameter and measure the run out on it, it will be different from the first pin. Same chuck, same DI, same everything, but the run out will change. The reason for this is because the jaws are clamping down in a different part of the scroll so run out varies with the diameter. This might not make sense but it is what it is. If you want to test it, chuck up some drills of varying diameters and test it yourself and you'll see.
The bottom line is that if your 3 jaw chuck is accurate enough to give you zero run out on a first op turning then that chuck is good to go. Use it for first operations only or when concentricity of the part is not important. Try not to use it for second op work; use a 4 jaw or collet for that.

Hope that helps.


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## GunsOfNavarone (Feb 23, 2020)

Thanks again Mikey, I'll be honest..I was worried about getting that chuck dead on center on the back plate..being that isn't such a concern, I'll move on and check run out the way you have laid out. Got so many iron in the fire right now, but at least I know I'm good to go on this chuck, that will reduce the amount I'm switching back n forth. Thanks everyone else that chimed in as well! Cheers!


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