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Stock alignment

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richard.nott

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#1
was trying to drill a 1/4" hole in some 3/4" round cold roll and find that it's half a hole off when the drill went through. the chuck is a three jaw align able scroll chuck. should I align the chuck first or put a piece of drill rod in the chuck an align off of it. appreciate the help Richard
 

RJSakowski

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#2
was trying to drill a 1/4" hole in some 3/4" round cold roll and find that it's half a hole off when the drill went through. the chuck is a three jaw align able scroll chuck. should I align the chuck first or put a piece of drill rod in the chuck an align off of it. appreciate the help Richard
If I understand you correctly, you have a Set Tru or similar three jaw chuck which allows you to zero any runout. That should be done with the stock in place.
I also understand you to say that it is the exit hole which is not concentric. This is a common problem when drilling holes with a large depth to diameter ratio. There are a number of factors which can cause this. The entrance hole not being concentric, the tailstock not being aligned with the spindle axis, a drill with unequal lips, flute loading, to name a few. Once a drill starts to go off center, the situation gets worse resulting in an exit hole that is considerably off center.
When I want my exit hole to be concentric, I will drill from either end with and undersized drill. I then follow with a slightly larger drill which will tend to straighten any irregularities in the middle of the piece. Then I will finish with my final diameter drill.
 

pacifica

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#3
You can start with a center drill, also, then follow procedure above. Use short feeds, there are formulas for how many pecks per distance from start.
clear chips out of hole .
 

richard.nott

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thanks for the help i'm going to recenter my stock and us your methods i'll reply after trying thanks
 

MrWhoopee

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You didn't say how long the stock is, but It is unlikely that the problem is the fault of the chuck or its adjustment. Unless the jaws are SEVERELY damaged, it's hard to get the stock cocked relative to the axis of the lathe. If the hole started on center and wandered off (which is a very common problem), it's usually the fault of the drill, tailstock or technique.
 

richard.nott

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the stock is 3/4" of and 1 13/32" in length I was trying to drill a 1/4" hole through it but it's wandering off center. i'm in the process of realigning the chuck and going to try again. i'm going to use a center drill and a new drill this time. i'm willing to work with it to get it correct. thanks for the advice.
 

P. Waller

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#7
If the hole runs out 1/8" over less then a 1 1/2" length you have a problem, try drilling from the tool post, if it improves this way it is the tail stock.

Contrary to what youtube how to videos will tell you live tooling is not required, it is exactly like drilling from the tail stock but the drill is held in the tool post, it may then be power fed, this is far less annoying then drilling with a tail stock but will be limited in the hole size depending on the machine. Set up is important but the time saved is well worth it with multiple parts. I use a QCTP holder with a drill chuck held in it, you may also buy tool holder blocks with a M Taper in them.

Like so, very handy to have about.
https://www.mscdirect.com/browse/tn...MIm46boeHZ3AIVyVuGCh3Tmwh_EAQYAyABEgKPl_D_BwE
 

richard.nott

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#8
guess i'll start in the beginning of my problem. my lathe is a 13x40 south bend built about 1964 and set for about twenty years before I got it about 7-8 years ago. my chuck that i'm using is a pratt-barnard 8 inch tru-scroll that came with the lathe. what i'm trying to do is drill a 1/4" hole through a piece of 3/4" crs 1 1/2" long per the suggestions that I've gotten here ( and many thanks) I went about the process of truing up the chuck with a piece of 1" drill rod in the jaws. this is a piece that I've made into a mandrel to help me with alignment. I loosened the six 1/4" allen cap screws that hold the body to the backing plate and was able to align the stock to within half a thousands of movement. BUT when I tightened up the cap screws it through it out of alignment to the figure of .005 either side of center. i'm not for sure where to begin would it help if I disassembled the chuck a gave it a good cleaning before trying to align it again because I have been noticing some hard turning when using the chuck key. any help a this point would be greatly appreciated. thanks for the help Richard
 

P. Waller

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#9
If the hole begins at one position at the face and is 1/8" offset at exit it is not the chuck, if your goal WAS to drill an offset hole through a round by offsetting the chuck both entrance and exit holes would have the same offset, think of a cam.

As mentioned above a very poorly ground drill bit will do this as well, before taking everything apart go and buy a bit not sold in big box hardware stores, OSG makes excellent drills however a 1/4" jobber length drill will cost close to $30.00 each retail, you can probably buy a 1/16 to 1/4 X 64ths SET for far less then half of that, do not do it.
 

pacifica

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guess i'll start in the beginning of my problem. my lathe is a 13x40 south bend built about 1964 and set for about twenty years before I got it about 7-8 years ago. my chuck that i'm using is a pratt-barnard 8 inch tru-scroll that came with the lathe. what i'm trying to do is drill a 1/4" hole through a piece of 3/4" crs 1 1/2" long per the suggestions that I've gotten here ( and many thanks) I went about the process of truing up the chuck with a piece of 1" drill rod in the jaws. this is a piece that I've made into a mandrel to help me with alignment. I loosened the six 1/4" allen cap screws that hold the body to the backing plate and was able to align the stock to within half a thousands of movement. BUT when I tightened up the cap screws it through it out of alignment to the figure of .005 either side of center. i'm not for sure where to begin would it help if I disassembled the chuck a gave it a good cleaning before trying to align it again because I have been noticing some hard turning when using the chuck key. any help a this point would be greatly appreciated. thanks for the help Richard
I wouldn't disassemble chuck; when you tighten the cap screws only tighten to medium firm, then adjust your chuck by lightly tapping with a plastic hammer . Then lightly screw down each of the cap screws, check concentricity, screw down each one a little more, check, then tighten completely. use a torque wrench for more control if you want. You might have to spend an hour or two to get it to .0001.Don't give up til it is good.
I am assuming high quality(holo-krome or unbrako) cap screws, flat surfaces ( less than .001") , burr free and clean on faceplate and chuck. Be sure shoulders on cap screw holes are clean and not scored.
 

Bob Korves

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#11
Scroll chucks are never exactly true over their full travel. The scroll is not a precision guide to the jaws even when new, and often worse if some previous operator used it a lot or abused it. Swarf in the scroll can also be a problem. I would take it apart and clean, inspect, and test it, so you know what you have.

Also, a set true type chuck will not be accurate or repeatable over it's entire travel. If you dial it in on a 1" part, then 1" parts should stay pretty close. But 2" parts can very likely be off, again because the scroll is not a precision piece. You have to reset the chuck for each diameter, and really for every new part put in the chuck if you are seeking high accuracy. That is why I just use my 4 jaw for almost every task. A set true three jaw is in reality just a three jaw being dialed in by a four jaw. I only really use my 3 jaw for chucking triangular or hexagon parts, or if I am doing a longer series of parts that do not need to be accurate.
 
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mikey

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I'm with Bob, Richard. I would personally take the chuck apart and clean it. Chips and crud can definitely affect how accurately a jaw clamps on the part. I don't think it would cause the kind of inaccuracy you are seeing but it contributes. With that said, having a hole come out as far off as your hole is, I am guessing the issue is not just the chuck but the drill itself or whatever is holding the drill.

Is the tailstock aligned with the spindle axis? Is the tailstock taper clean and in decent shape? Is the drill chuck mounted accurately on a decent arbor?

If the chuck was at fault, the hole would come out larger and out of round but for the hole to come out off axis ... that is on the drill end, not the chuck end.
 

Bob Korves

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If the chuck was at fault, the hole would come out larger and out of round but for the hole to come out off axis ... that is on the drill end, not the chuck end.
That makes sense, Mike.
 
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