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  1. #1
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    Question quick change collet chuck selection for Doosan CNC lathe ...

    We just bought a Doosan 2600SY CNC lathe with 77mm (~3.03") bar capability on the main and 50mm (~1.97") bar capability on the sub. We want to install a pair of collet chucks that allow the use of quick change collets and S-series master collets and top pads. We plan to run a servo-style 4' bar feeder on the machine. We're getting quotes from Microcentric, Royal, and Hardinge and want to ask a few questions so weíre not disappointed with our choice. Iíve read about a bunch of threads on the forum on quick change collet chucks, and I didnít really see these questions answered, so thanks in advance to anyone who can answer from experience...

    1. We were planning to go with an 80mm (3.15") collet chuck on the main and a 65mm (2.56") collet chuck on the sub, but we see that Royal offers 80mm chucks for the A2-5 spindle nose on the sub. Since our sub has a fairly sophisticated parts ejector installed (that we donít want to remove), is it worth considering going with the 80mm collet size on the sub at the expense of more expensive collets and a larger chuck nose? Or would you suggest sticking to a smaller collet chuck on the sub and when necessary cut emergency collets or reinstall the regular chuck and just cut soft jaws?

    2. We were planning to buy dead-length chucks for both the main and sub, but I read many posts stating the dead-lengths are not as accurate (understood due to more moving parts) and possessed lower clamping force. I can understand them being less rigid due to the additional moving parts, but can aggressive turning or drilling in tougher materials really overcome the drawbar pushing force, causing the material to slide back in the collet significantly more than pull-back style chucks? And if so, are serrated collets or top pads adequate to prevent this, or is a pull-back style chuck the only solution? Iím not trying to take 1/2" depth cuts or feed at 0.02 ipr with a 2" indexable drill in cobalt chromium, but I donít want to have to baby a 30hp machine either. My interpretation of the threads Iíve read about this question is that modern dead-length chucks should be fine, and if you need more, use serrated hardened top jaws on the factory 3 jaw chuck.

    3. In hindsight, were there any surprises / disappointments with the quick change chucks you purchased that would change your purchasing choice if you had it to do over?

    Thanks!

    Mike

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    Quote Originally Posted by mbraddock View Post
    We just bought a Doosan 2600SY CNC lathe with 77mm (~3.03") bar capability on the main and 50mm (~1.97") bar capability on the sub. We want to install a pair of collet chucks that allow the use of quick change collets and S-series master collets and top pads. We plan to run a servo-style 4' bar feeder on the machine. We're getting quotes from Microcentric, Royal, and Hardinge and want to ask a few questions so weíre not disappointed with our choice. Iíve read about a bunch of threads on the forum on quick change collet chucks, and I didnít really see these questions answered, so thanks in advance to anyone who can answer from experience...

    1. We were planning to go with an 80mm (3.15") collet chuck on the main and a 65mm (2.56") collet chuck on the sub, but we see that Royal offers 80mm chucks for the A2-5 spindle nose on the sub. Since our sub has a fairly sophisticated parts ejector installed (that we donít want to remove), is it worth considering going with the 80mm collet size on the sub at the expense of more expensive collets and a larger chuck nose? Or would you suggest sticking to a smaller collet chuck on the sub and when necessary cut emergency collets or reinstall the regular chuck and just cut soft jaws?

    2. We were planning to buy dead-length chucks for both the main and sub, but I read many posts stating the dead-lengths are not as accurate (understood due to more moving parts) and possessed lower clamping force. I can understand them being less rigid due to the additional moving parts, but can aggressive turning or drilling in tougher materials really overcome the drawbar pushing force, causing the material to slide back in the collet significantly more than pull-back style chucks? And if so, are serrated collets or top pads adequate to prevent this, or is a pull-back style chuck the only solution? Iím not trying to take 1/2" depth cuts or feed at 0.02 ipr with a 2" indexable drill in cobalt chromium, but I donít want to have to baby a 30hp machine either. My interpretation of the threads Iíve read about this question is that modern dead-length chucks should be fine, and if you need more, use serrated hardened top jaws on the factory 3 jaw chuck.

    3. In hindsight, were there any surprises / disappointments with the quick change chucks you purchased that would change your purchasing choice if you had it to do over?

    Thanks!

    Mike
    I have a s26? dead length collet chuck on my Miyano for get the brand but its from germany and expensive. I love it dead nuts accurate in both run out and length. the problem is , using it as a barfeed chuck. as when its clamping it pushes out (opposite than a normal chuck that pulls in) what happens is if you use a Hard stop it puts a ton of pressure on your turret and even marks your part up at times.

    The problem with s style chucks the big collet ones with pads is that you will get a ton of chips building up in the Especially the dead length ones. so you need to run a bead of silicon on the master collet holes and slots of keep the chip from getting in between the collet chuck it self.

    we had a job 7 years ago that we made about 20k alum parts 2nd op with a small thru bore and a decent sized counter bore. the 1st 1k parts were apain in the ass due to chips in the collet mechanism. onces we did the silicon or rtv we didnt have any issues.
    like wise on op 10 the bar feed one we ended up using delrin for out hard stop to keep the chuck from putting so much pressure on the turret when closing. A hard rubber bumper screwed into a solid bar stop works good also.

    so keep that in mind when you start using them. I have a hydrailic bar feed so it wont be the same with the barfeed your getting on the haard stop in the chuck. but the send up stuff with thru holes will get your attention quick if you dont seal them tight.

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    We use dead-length Royal Quick Grips, QG80 and QG65 on the main and sub, respectively. Machine is a DMG Mori NLX2500SY, 80mm drawtube. You can see them in action in our latest youtube video and you'll see how they look in terms of size. I was temped to go with a QG100/QG80 combination because we have parts that go up to 4" OD, but decided otherwise due to clearance issues.

    We use Royal's ejector in the QG65. It can be installed or removed in a few seconds.

    If you use pullbacks, the part may drag in one of the collets during transfer. It was my understanding when I bought the chucks that I didn't really have a choice as to style. Subspindle machine = dead length chucks. It's not just Z-length control of the part, but also not scratching the finished surface of the part during transfer. Perhaps someone else can chime in if they've done/seen otherwise.

    I haven't had an issue with part slippage except for situations where I'm not gripping the part along the full length of the collet, and that typically only happens on the sub. The problem is compounded by the fact that naturally, the sub collet is going to be smooth, as it's gripping a machined surface.

    To avoid slippage on the main, yes, use serrated collets if you think it might be an issue.

    Fast forward to 2:29:


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    Thank you both for your insightful comments. Your feedback should help me make the right choice.

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    Hardinge is currently running a big sale on their Flex-C collet chucks, I think its 5 free collets and the gripper if you buy 1 chuck.
    I wish they had that deal 2yrs ago when I got mine.

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    We have a few lathes with this style chuck on it and I will say after the first one we went with all dead lengths. The reason being, if you do a part transfer as a single transfer from main to sub I have never had an issue. Then I needed to do a longer part that required going from the main to sub twice (had to re-grip to get far enough towards the end) and that became an issue. When doing that I was now holding the part in the dead length sub chuck while trying to re-grip wit my pull back main. That pulls against the sub spindle when you do that as it closes.After that any other machines were dead length on both sides in case that situation presented itself again.

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