How snug should the carbide collet be?



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    Default How snug should the carbide collet be?

    I'm new to swiss, and I didn't get the manuals with this machine.

    How snug should the forward collet be adjusted? Should it be a slip fit, or slightly tight?

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    Default Re: How snug should the carbide collet be?

    The "Carbide collet" is called a Guide Bushing on Swiss machines.

    The tightness of the GB is a "magic feel" you will develop over time. Its dependent on:
    how consistent your stock is
    what tolerance you're trying to hold
    how large the stock is
    stock material
    probably a couple other factors too.

    In general, I set my guide bushings so that you can move the bar back and forth with a firm grip with moderate resistance (meaning it takes about 50% of my strength to slide the stock). For smaller stock, a 1 or 2 finger pinch may be all that is necessary. For larger stock, a firm grip and nearly full muscle strength may be needed.

    Things to consider:
    If you are using non ground stock, you need to mic the bar and find the high spot, then set the tension on a high spot. Otherwise you can jam up or pretzel the stock between the collet and bushing. If you are using ground stock or your stock is very consistent, you can set it tighter.

    How closely does the GB diameter match your stock diameter? your stock should never be larger than your GB nominal bore, and no more than -.001 ideally. (I have gotten away with -.002 to -.005 in extreme cases where I just had to make something work, but its far from ideal to compress a bushing more than .001"). accuracy decreases, runout increases as your stock goes undersized compared to the bushing.

    What tolerance are you trying to hold? if you're trying to hold +0 -.0003", your bushing will need to be tighter than if you have ±.001. Same goes for ±.005.

    How big is your stock? I made a lot of parts from .060 stock and would pinch the stock between my thumb and pointer finger. If I couldn't slide it with just a 2 finger grab, it was too tight and would pretzel. In general, stock below .156" requires more attention to tightness. once you're at .250 and above, the stock wont really pretzel, but there are other considerations like...

    What's your material? certian materials like to Gall on the leading edge of the bushing. Once it starts, it basically never stops until it galls too much and your Z1 servo's out. At that point you have to back up the spindle and hack saw off the galled stock. Stainless steels and Tool steel likes to gall, among others. If you have a galling material, set it slightly looser or break the leading edge of the carbide pad with a diamond tip on a dremel.

    That should get you started. Basically I would say shoot for 'moderate resistance'. Though that is subjective, to me that means for a medium size stock (.250 - 1.0") you shouldnt be able to move it with a 2 finger pinch. Also, you should be able to slide it with a 5 finger grip with about 25-50% of your maximum strength. In some cases, it had to be so tight it required the spindle to force it through, though that was uncommon.

    Hope that helps.

    CNC Product Manager / Training Consultant


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    Default Re: How snug should the carbide collet be?

    MCImes,

    Thank you!!!

    Your description was excellent. I assumed the same, but I wasn't sure. Again...Thank you! I called Alro and asked them if they had Swiss ready brass. They said that thier brass is already to tolerance. We'll see. The machine has 1/2" collets in it...I bought a bar of brass and cut it into 3' sections in order to try some of the programs that were still in the control. I did adjust the guide bushing to a slight drag and it worked great! I love this machine...It is capable of sooo....much!

    Last edited by 91Tsugami; 10-16-2017 at 06:25 PM.


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    Default Re: How snug should the carbide collet be?

    Shop Doc – Chatter while turning on 20mm Swiss CNC Lathe | Today’s Machining World

    i will add that guide bushing tension is alot of personal prefrence too, when i ran alot of aluminum we would set it to where when we spun the bushing it would drag but not turn on the bar. now a days i use the barfeed servo as my guage, if i can push it in with the barfeed and push it back by hand thats my start point.

    also watch your z load meter it can give you a good indication on where your tension is.

    and finally i cant stress enough, buy good material. the fastest way to crash a swiss is too have a guide bushing lock up and a main slip and all the sudden your part is 1/2" longer and your .040 clearance move is now inside the part



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    Default Re: How snug should the carbide collet be?

    and finally i cant stress enough, buy good material. the fastest way to crash a swiss is too have a guide bushinglockup and a main slip and all the sudden your part is 1/2" longer and your .040 clearance move is now inside the part

    Yep, I managed to do exactly this...LOL. Fortunately I was at the machine when it happened, and hit cycle "stop" before a crash happened! There was a .001" difference from one bar to another. I now mic each bar, and adjust the bushing accordingly. I've been running 360 brass. Each 12' bar has been within tenths, but from bar to bar the diameter definitely varies. I normally get my material from Alro, but they don't offer 360 brass that has been centerless ground. Copper & Brass sales does, so I will be getting my next batch of brass from them.

    Thanks for the advice!

    It has been a definite learning curve setting up and programming this machine. I've been programming mills since the eighties, but never a Swiss. I still don't have the G&M codes to program the live tool turret. The manual is on the way.



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    Default Re: How snug should the carbide collet be?

    The tooling should be set at least 3/4 of the depth of the collet. Setting the tool the full depth of the collet is best, If possible.

    A snug fit on the collet diam is all you need when test fitting the tooling inside a collet outside the holder.

    Always inspect the collet for cracks. If you find cracks in the collet odds are the collet diam. is too big for the tool. The slits in a collet allow it to compress and hold the tooling tight, you don't want those slits fully compressed against each other, that causes cracks in the collet when tightened down.

    Forcing a tool too large inside a collet can also cause cracks in a collet.

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How snug should the carbide collet be?

How snug should the carbide collet be?