Citizen Cincom L20, second spindle leaving marks on workpiece
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  1. #1
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    Default Citizen Cincom L20, second spindle leaving marks on workpiece

    Hello,

    we're turning tiny parts, with clamping diameters <1.9-2.1 diameters and relatively short clamping lengths of ~1~mm and its often even less than that.

    Probably the biggest issue is the marks on a workpiece when its clamped by second spindle before cutoff. There aren't many people around that has
    experience when working with such tiny pieces and as I heard there are people who even refuse to work when similar kind of pieces with tiny lengths of
    clamping surface is required.

    So as searching for similar information on the internet does not seem to provide much more than this post
    swiss-type lathes

    which ofc had some useful information, but not too much.

    As not of forums but collet sellers like schlenker brags about their L-slot or S-slot collets, which turned out to be quite a disappointment, because
    L-slot collet came with just a very tiny L-like curve that does not seem to be efficiently bent, its nearly straight.

    S-slot is just plainly leaving marks and it seems that it was covered with anti-sieze grease or something.

    It would be interesting to hear something from people who had to deal with similar lathes and small parts. Because the information on the internet about it is a bit lacking. Especially when clamping tightness is adjusted by feeling. One must be sensitive enough to micro-degrees.

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    So....collet is definitely burr free and smooth etc?
    Not overpressure of S2?
    Synchronisation not matched between S1 + S2?

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    You may benefit from making a collet that can retain a small acetal resin bushing that has a bore slightly larger than the part you work with. The collet collapse would shrink the plastic bushing enough to hold your part, and it would prevent damage once you figured out the hole size and clamping pressure required.

    Downsides are expected wear that might require replacement of the bushing after (for instance) 1000pcs or so. You could try harder or softer plastics, but too soft and it might deform prematurely.

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    You can get pickoff collets made of Delrin, the company that makes them is Neukomm, I buy them through Floyd Automatic in the UK. Any of the major manufacturers will make you a pickoff collet that has a liner of delrin or brass or meehanite, all softer materials that shouldn't mark your parts. But, are you positive your sub spindle is aligned to your guide bushing? If the marks are occurring at pickoff, and not due to back work operations, I'd suspect your sub spindle and guide bushing aren't aligned. What's your pickoff procedure? How fast are you spinning the part when you clamp the sub spindle? Are you sure your sub spindle and main spindle are synced (M77?). Another option is the MASA Microconic collet system, which requires a cartridge and a collet. The up side to these is that pressure is not set by "feel", you use a gage pin, and a graduated wrench to set collet pressure, so that your results are repeatable and reproducible across multiple setups. Of course, you can use gage pins to set a standard collet, as well, it's just a bit slower and less repeatable.

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    Quote Originally Posted by TeachMePlease View Post
    You can get pickoff collets made of Delrin, the company that makes them is Neukomm, I buy them through Floyd Automatic in the UK. Any of the major manufacturers will make you a pickoff collet that has a liner of delrin or brass or meehanite, all softer materials that shouldn't mark your parts. But, are you positive your sub spindle is aligned to your guide bushing? If the marks are occurring at pickoff, and not due to back work operations, I'd suspect your sub spindle and guide bushing aren't aligned. What's your pickoff procedure? How fast are you spinning the part when you clamp the sub spindle? Are you sure your sub spindle and main spindle are synced (M77?). Another option is the MASA Microconic collet system, which requires a cartridge and a collet. The up side to these is that pressure is not set by "feel", you use a gage pin, and a graduated wrench to set collet pressure, so that your results are repeatable and reproducible across multiple setups. Of course, you can use gage pins to set a standard collet, as well, it's just a bit slower and less repeatable.
    happen to know rough prices on that MASA cartridge and collets ? because it is something that we got into our attention, but schlenker somewhat failed to answer about it in a single email with multiple different sorts of questions. Floyd Automatic is also something I've browsed, but they simply just haven't responded to an email same as iswiss, maybe they are skeptical to EU clients.

    Spindles get synced, yes. Programs are CAM'ed using ESPRIT, so its a bit less error prone than manually typed ones, so this issue is not in a program. Pickoff procedure is something like this and is generally the same:
    ----------------------------------------------------------------------------
    M16 (back spindle chuck open)
    G0 Z-3.
    M77 (wait until spindle synchronization is completed)
    G1 G98 Z7.5 F1000. (mm/min)

    G99 (mm/rev)
    G4 U0.5 (dwell)
    M15 (back spindle chuck close)
    ----------------------------------------------------------------------------
    Thing is that if spindles would not be properly aligned, I suspect markings would be on all kinds of parts, but this marking is most troubling on smallest parts as defined in original post as at the moment I'm making parts that are about 3.6mm diameter and has a lot of surface to clamp on, theres little trouble to adjust clamping for such parts.

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    About 3K for the cartridge and about 300 per collet.

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    Quote Originally Posted by PovilasCNC View Post
    Floyd Automatic is also something I've browsed, but they simply just haven't responded to an email same as iswiss, maybe they are skeptical to EU clients.
    Floyd are among the most friendly and helpful vendors I've dealt with. Even if they didn't want to deal with you for some reason I would not expect them to simply ignore you. Just about everything they sell is manufactured within the EU, so I highly doubt they are reluctant to sell back to EU clients.

    Most likely they are suffering the same problem as everyone else in the UK, with employees being required to stay at home for 7-10 days any time they or a family member fail a lateral flow test. It's incredibly fucking difficult to run a business in the UK at the moment, and everyone is short-handed.

    Politics aside, it's very unlikely they are deliberately ignoring you, persevere, and surely they will respond eventually.

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    I occasionally have this problem on smaller shorter parts especially if it's a soft material like aluminum or has a thin wall. In the case that you choose not to go with options already presented such as softer collet material etc..I can offer you this...

    1) Lightly debur all edges of the collet coming in contact with the part. Most times your part will show you which areas of the collet are contacting it.
    2) I have actually lapped a sub collet because the roundness/ID during gripping was off from the actual part size. This was a big help. I made the lapping tool the same size as my part OD then slapped on some lapping compound and went at it. Got rid of the high spots that were biting into the part OD.
    3) Slow down RPM during pickoff.
    4) Slow down cutoff tool feed.
    5) Your collet may be too tight. Often times, this is the simplest overlooked root cause. Lessen your collet grip and precisely set it. For example. Set your collet with a gage pin or part to your desired pressure. Then close the collet and see if a gage pin .002 smaller than the set size will slide into the collet. If not, then you might consider that too tight and need to readjust. You pick the value of how much smaller you want it and use that as your reference for future set ups.

    I have implemented all of these sometimes by themselves and sometimes in combination and it's usually enough to resolve the problem without having to purchase additional tooling.

    Best of luck.


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