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Chuck Run-out
- Thread starter ddickey
- Start date
I got my linear motion shaft today. I got a 1 1/4" x 12" & a 1/2" x 6". I tried the larger diameter at 8" run-out was .015" at 2" it was .010"
I was thinking if I get a chance tonight I'll try rotating the shaft 120° (in the chuck) and see if that changes anything.
I was thinking if I get a chance tonight I'll try rotating the shaft 120° (in the chuck) and see if that changes anything.
- Joined
- Dec 20, 2012
- Messages
- 9,422
Have you checked the concentricity of your spindle? I find that information more useful than knowing a 3 jaw chuck is running out by X-amount. The reason is that if you turn a piece in a 3-jaw chuck and do not remove it then it should run very near or at the concentricity of the spindle if the chuck is in serviceable condition. If it does not run accurately then that would suggest you have an issue with the chuck somewhere - jaws worn, scroll worn, etc.
The other thing to consider is that runout of a scroll chuck is typically established at the factory by tightening only one jaw and this jaw is usually marked with a dot, a zero or some other identifier. To find out if the chuck is running within specs you have to lock an accurate test rod in the chuck and tighten it at that designated pinion socket. Otherwise, the specs don't apply. Lots of guys tighten the chuck at all three pinions, which has the potential to throw the accuracy of the chuck out.
The other thing to consider is that runout of a scroll chuck is typically established at the factory by tightening only one jaw and this jaw is usually marked with a dot, a zero or some other identifier. To find out if the chuck is running within specs you have to lock an accurate test rod in the chuck and tighten it at that designated pinion socket. Otherwise, the specs don't apply. Lots of guys tighten the chuck at all three pinions, which has the potential to throw the accuracy of the chuck out.
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I did check the spindle when I had the chuck off. There was very little if any run-out. I think it was .0005". I did notice some spindle movement when I had my test piece in yesterday and lifted up on the piece. Didn't have time yesterday to check other positions. Will be gone this weekend so may have to wait until late Sunday.
I checked the spindle and virtual no run-out. I did however make a mistake on my measurements yesterday. My dial was not in contact the entire revolution so was not getting a true reading. Run-out is ~ .045" I rotated jaws and also changed every cam lock position. The least I could achieve was .037" max was .055". It was not repeatable though when I went back to recheck.
So I have a couple questions.
1. Is it correct that run-out doesn't matter as long as the part is not removed from the chuck?
2. Would new jaws make any difference?
3. Do four jaw chucks have run-out? In other words, can most of the run-out be adjusted out.
4. At this point should I care? I've completed one thing so far (captive nut) and only ever made two other metal projects, (dead center & carriage stop).
My next project will be a machinist clamp.
So I have a couple questions.
1. Is it correct that run-out doesn't matter as long as the part is not removed from the chuck?
2. Would new jaws make any difference?
3. Do four jaw chucks have run-out? In other words, can most of the run-out be adjusted out.
4. At this point should I care? I've completed one thing so far (captive nut) and only ever made two other metal projects, (dead center & carriage stop).
My next project will be a machinist clamp.
- Joined
- Dec 20, 2012
- Messages
- 9,422
Let me take a shot at this and the others can chime in and correct me.
First, be sure you checked the concentricity of your spindle correctly. That is, run the lathe for 20 minutes or so at moderate speed to warm it up, then shut it off and shift into a gear that allows you to easily turn the spindle by hand. Clean the taper inside the spindle so it is oil and dust/dirt-free and then use a solidly mounted DTI of adequate sensitivity (0.0005 works) and lightly preload the tip with about 0.015" of pressure before zeroing the dial. I usually place the tip at 6 O'clock so I can see the dial easily. Place a mark with a Sharpie on the spindle mount at 12 O'clock and then slowly make one complete revolution, returning the mark to 12 O'clock; the dial should return to zero. If so, then slowly rotate another revolution but look for any deviation from zero and this will be the run out of your spindle. When you do this, make sure you turn the spindle in one direction only. If you are doing this any other way then your results are going to be variable. Concentricity is NOT checked with the spindle running.
To figure out how to clock the chuck, lock an accurate test pin in the chuck and lock it down with the factory-marked pinion (as mentioned above) and check the concentricity of the pin. Normally, I put the tip of the DTI at 12 O'clock, perpendicular to the test pin and very near the chuck jaws. Do the same thing - make one revolution to be sure the dial returns to zero and then another to check how much run out you have and write it down. Now remove the chuck, turn it so the next D1 pin lines up, lock the chuck onto the spindle and re-test the run out as above. One position will give the least amount of run out and that is the position you should always install your chuck in. Most spindles have a witness mark somewhere on the spindle mount; make a corresponding mark on the chuck right across from it so you can install the chuck the same way every time.
As to your questions:
1. If you don't remove the part from the chuck and your chuck is in decent shape (jaws and scroll are okay, no major issues) then the part will have the same runout as your spindle, plus a little more due to cutting loads. It should be at or very near the spindle run out unless your spindle bearings are shot. The amount of "run out" your chuck has with a test bar has little to do with your actual results. Bear in mind that if you take the part out of the chuck and then try to get it back in place then your run out will be greatly magnified.
2. Not unless your current jaws are damaged.
3. 4 jaw scroll chucks do. 4 jaw independent chucks will have as little run out as you have the patience to dial out. It is possible to dial out almost all the run out in a 4 jaw chuck but it can take a few minutes to a few hours, depending on the phase of the moon or the current wind direction. Some days, God just smiles on you ...
4. It is important to assure accuracy when it counts. The trick is to know when that is. In the case of your 3 jaw chuck, I would just accept that it cuts adequately and move on to learning to run the lathe or how to grind a good tool.
Bear in mind that there are adjustable 3 jaw chucks called Adjust-tru chucks and they can be adjusted to run very accurately, enough to satisfy most folks. I don't own one; I use ER collets when I need that kind of accuracy.
As hobby guys we tend to obsess about accuracy and will move the earth to cut something with tenths accuracy BUT there are times when you should do this and times when you don't, and most times you don't. Set a reasonable tolerance expectation and learn to hit it. Otherwise you will spend more time fiddling and less time making stuff and that's what this is all about, right? Making stuff.
Mike
First, be sure you checked the concentricity of your spindle correctly. That is, run the lathe for 20 minutes or so at moderate speed to warm it up, then shut it off and shift into a gear that allows you to easily turn the spindle by hand. Clean the taper inside the spindle so it is oil and dust/dirt-free and then use a solidly mounted DTI of adequate sensitivity (0.0005 works) and lightly preload the tip with about 0.015" of pressure before zeroing the dial. I usually place the tip at 6 O'clock so I can see the dial easily. Place a mark with a Sharpie on the spindle mount at 12 O'clock and then slowly make one complete revolution, returning the mark to 12 O'clock; the dial should return to zero. If so, then slowly rotate another revolution but look for any deviation from zero and this will be the run out of your spindle. When you do this, make sure you turn the spindle in one direction only. If you are doing this any other way then your results are going to be variable. Concentricity is NOT checked with the spindle running.
To figure out how to clock the chuck, lock an accurate test pin in the chuck and lock it down with the factory-marked pinion (as mentioned above) and check the concentricity of the pin. Normally, I put the tip of the DTI at 12 O'clock, perpendicular to the test pin and very near the chuck jaws. Do the same thing - make one revolution to be sure the dial returns to zero and then another to check how much run out you have and write it down. Now remove the chuck, turn it so the next D1 pin lines up, lock the chuck onto the spindle and re-test the run out as above. One position will give the least amount of run out and that is the position you should always install your chuck in. Most spindles have a witness mark somewhere on the spindle mount; make a corresponding mark on the chuck right across from it so you can install the chuck the same way every time.
As to your questions:
1. If you don't remove the part from the chuck and your chuck is in decent shape (jaws and scroll are okay, no major issues) then the part will have the same runout as your spindle, plus a little more due to cutting loads. It should be at or very near the spindle run out unless your spindle bearings are shot. The amount of "run out" your chuck has with a test bar has little to do with your actual results. Bear in mind that if you take the part out of the chuck and then try to get it back in place then your run out will be greatly magnified.
2. Not unless your current jaws are damaged.
3. 4 jaw scroll chucks do. 4 jaw independent chucks will have as little run out as you have the patience to dial out. It is possible to dial out almost all the run out in a 4 jaw chuck but it can take a few minutes to a few hours, depending on the phase of the moon or the current wind direction. Some days, God just smiles on you ...
4. It is important to assure accuracy when it counts. The trick is to know when that is. In the case of your 3 jaw chuck, I would just accept that it cuts adequately and move on to learning to run the lathe or how to grind a good tool.
Bear in mind that there are adjustable 3 jaw chucks called Adjust-tru chucks and they can be adjusted to run very accurately, enough to satisfy most folks. I don't own one; I use ER collets when I need that kind of accuracy.
As hobby guys we tend to obsess about accuracy and will move the earth to cut something with tenths accuracy BUT there are times when you should do this and times when you don't, and most times you don't. Set a reasonable tolerance expectation and learn to hit it. Otherwise you will spend more time fiddling and less time making stuff and that's what this is all about, right? Making stuff.
Mike
- Joined
- Jun 29, 2016
- Messages
- 16
The new 3 jaw chuck I purchased has maximum acceptable TIR of 0.0016". Older chucks will most likely have more. Even if you have a Set-Tru chuck it will only be right on for the size stock that you used to set it. If I need to turn something true to center I use the 4 jaw chuck.
Tim
Tim
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These Chinese 3-jaw chucks are not the greatest chucks out there, but are ok. I have a Chinese 6" 3-jaw chuck with 2-piece jaws I bought about 14 years ago. First thing I did was take it apart and thoroughly clean out all of the grinding grit and that strange Chinese grease that was impregnated with grit too. Borrowed some Texaco grease with moly from work and lightly greased the scroll a gear and re assembled. With the chuck fitted to the back plate I made, the best runout I could get was .003" at the chuck. To get it closer, I turned off about .005" off the diameter of the register on the back plate and re-mounted the chuck. With my H & G dowel pin I use, I was able to bump around the OD of the chuck and got it within about .00025". Tighten down the three cap screws and rechecked runout, no change. Out about 4" from the chuck, runout was about .002". I can live with that. For most of the stuff I work on, it is within 1" of the chuck jaws. I have had to readjust the alignment a couple of times over the years, too, but that is expected, especially at different diameters. I have to do that on my adjuster-true chucks on my other lathes, too. Ken