plead for 3 jaw chuck knowledge

[mikey]

Every high quality chuck I've seen has numbered jaws and jaw slots. Typically, the factory will hand fit the jaws to make sure the jaw fits without binding before numbering them. Some chucks, like Rohm, will fit the jaws and certify the accuracy of the chuck by tightening only one pinion; that pinion will be marked and the chuck should be tightened onto the work with that pinion. Otherwise, the accuracy of the chuck may not fall within specs.

The point: if your jaws are numbered then use them as marked. If not, then as long as the jaws fit without binding it should be okay. If you want the best accuracy from them, swap the jaws and check run out with a dowel pin until you find the best combination, then mark them yourself and mark the pinion that produced that best result. Once done, it should hold the tolerances the combination can produce.

 

[Rustrp]

Casca, try looking at this thread: http://www.hobby-machinist.com/threads/chuck-run-out.50125/

I showed some pics on how the jaws of a 3JC are installed. Does this help?

So the link took me back to the older thread and it's all good stuff. -Russ

 

[Rustrp]

Remember chips this is a HOBBY forum; lots 'o folks here
(myself included) do just fine with the cheap-o chucks. I can get work within a thou with
my little chinese sow's ear with a bit of tapping.
Mark S.

I agree, but what chips&more posted is correct. If someone is on here as a hobbiest or machinist who worked in a facility that only bought less than quality or precision they wouldn't know. When people don't know, a lot of opinion gets pushed and passed along, and we get a lot of what I call backyard fence mechanics. i.e. The neighbor knows a neighbor who said do it this way and so on. **That's good enough** is okay for anyone who chooses to work this way but knowing how to make it a couple steps better is never a bad thing. I get on my soapbox about imports but it's the cheap imports which I'm referring and if a person wishes to go there that's okay, but with the correct information they can quit struggling with why they don't hit tolerances.

 

[chips&more]

I agree, but what chips&more posted is correct. If someone is on here as a hobbiest or machinist who worked in a facility that only bought less than quality or precision they wouldn't know. When people don't know, a lot of opinion gets pushed and passed along, and we get a lot of what I call backyard fence mechanics. i.e. The neighbor knows a neighbor who said do it this way and so on. **That's good enough** is okay for anyone who chooses to work this way but knowing how to make it a couple steps better is never a bad thing. I get on my soapbox about imports but it's the cheap imports which I'm referring and if a person wishes to go there that's okay, but with the correct information they can quit struggling with why they don't hit tolerances.

You nailed it! And we also get what I call “internet authors”. The people that sit in front of a key board typing away with misinformation, know-it-alls that don’t really have a clue or they could be just typing to be typing because they are bored.

 

[Rustrp]

You nailed it! And we also get what I call “internet authors”. The people that sit in front of a key board typing away with misinformation, know-it-alls that don’t really have a clue or they could be just typing to be typing because they are bored.

Good information is exactly that, it's good and it shouldn't be bad for anyone. So due to this conversation, I had to go out to the shop and crank out the jaws on the old lathe. It's a three jaw and I couldn't remember what my father-in-law told me was the correct order away from the brand stamp in the face of the chuck, CW or CCW. With the info he gave me I knew it would be one of the jaws on top where I positioned the brand, which is a Gisholt BTW. The way he expalined it was the #1 would drop in first as you face the chuck and rotate it clockwise. The first slot past the brand stamp is #1` and the #3 is to the right of the brand and goes in last. The jaws are numbered and I'm guessing the chuck is as old as the lathe, late 1800's to early 1900's.

Edit; The information was given a long time ago but I knew the first jaw to pop out would be #3.

 

[Rustrp]

ahh a light is starting to come on , not real bright but that is some guidance I was hoping for.

I'm a neopyte in the machinist occupation, so with everything stated you have three jaws with three different thread amounts. The #1 would have the most threads and the #3 the least.

 

[mikey]

A 3 jaw chuck is a 3 jaw chuck. It will have some run out; even the best chuck do. However, the run out is of little consequence as long as the part is not removed from the chuck; it will always be concentric with the spindle as long as we don't unclamp it from the chuck.

Run out values matter when we try to re-chuck a piece that is already turned. In this instance, an adjust-tru type chuck will get the part as concentric as possible for that specific diameter only. Otherwise, an adjust-tru chuck is like any other 3 jaw chuck.

I think it is always a good idea to buy a good chuck, primarily because the quality of the machining is better, tolerances in construction is tighter and they tend to function better for a longer period of time. However, this has little to do with concentricity of the results when you first turn a piece. As long as the chuck holds the work solidly and does not allow it to shift, a cheap Chinese chuck will be just as good as my Rohm/Emco/Samchully chucks on a first turning.

Hobby guys have various financial capabilities and Chinese chucks that hold solidly are just fine, in my opinion. I don't expect them to hold up as long or as consistently as a better chuck would but for hobby guy, I think that's okay.

 

[Superburban]

Thank you for stepping back in Mkiey. For a few minutes there I thought this had turned into a rich mans only board, and us on limited budgets were not wanted.

I'm a neopyte in the machinist occupation, so with everything stated you have three jaws with three different thread amounts. The #1 would have the most threads and the #3 the least.

I beg to differ. Not the number of threads, but the position like has been stated a few times already.

 

[RJSakowski]

I have often thought that if someone told me that they would give me a million dollars to spend on equipping a shop not including the building, on the condition that I had to spend it all within 24 hours that I could do it.

Unfortunately, I have a limited budget for equipping my shop. When I am considering purchasing new equipment, I always ask myself "Is it enabling?". By that I mean will it allow me to do something that I couldn't accomplish with my existing equipment. I bought my Tormach for that reason. I had projects that couldn't be accomplished by any other means.

I could spend $1K to 2K on a quality name brand chuck but it wouldn't enable to do anything that I can't do already. Spending that money on a TIG welder or plasma machine will permit me to take on projects that would be difficult if not impossible otherwise. I recognize the value of quality equipment and if this were my livelihood, it would be prudent to invest in same. But it is not my livelihood.

We have seen many examples of exquisite workmanship turned out on machines that would be considered toys at best by professionals and I personally have seen junk work come off quality machines.

 

[RJSakowski]

To further clarify the order in which chuck jaws are reinserted, here is a photo. Line the jaws up so they are all even and the distance of the tooth to the inside of the jaw is increasing. The jaws will now be in their correct order.

The chuck jaw with the tooth nearest the inside of the jaw (the left one, in this photo) is the first jaw seated. I place the jaw in the slot and turn the scroll backwards while maintaining gentle inward pressure on the jaw. At some point, the jaw will come off the scroll and drop down to the next position on the scroll. Turn the scroll forward to engage the jaw. Now insert the second jaw in its slot and continue turning the scroll until it captures the jaw. Repeat the process for the third jaw. The jaws will now be in their correct orientation.