Please advise: Swiss turned plastic parts. Appropriate applicaiton for swiss turn?

[MadMax]

I'm considering buying a swiss lathe to run some longer small diameter parts which are difficult on a larger fixed headstock lathe. Does anyone here have much experience with turning acetal parts in their swiss lathes?

How much oil are you losing on your chips? I find that plastics hang onto oil. I've been rinsing off my plastic chips with my makeup water to recapture my water soluble coolant, but I wouldn't be able to do the same with oil.

Is it possible to centerless grind delrin? I've never heard of ground plastic bar stock. I'm not sure I can get the bar ground for my shop. I typically need 0.0005" repeatability on my parts. Do I really need my bars to be ground? Can I sort out my bars by diameter and make guide bushing adjustments between size ranges?

What kind of changeover time should I expect between parts with different stock diameter? I think that most of my parts are quite simple and could be done with a nearly standardized tool set so I'm not too worried about tooling setup time, but I have no idea how long it would take to change out spindle liners and collets in a swiss lathe. How long does it typically take to adjust a guide bushing and other important parts to set up for a bar diameter change?

Thanks for your help guys. I appreciate the great info I got here for my first production acquisition. Now I find myself wanting another machine to opening up some new capabilities for my shop.

[danrudolph]

Delrin is a dream on my swiss. I am making some .26"dia by 2.25" long parts and they scream. We do not run coolant at all. The residual oil left from the bar feed is the only oil we need to clean off the part. Delrin parts should be cleaning in pure alcohol because it will absorb water and swell. The only problem with holding .0005 would be that the parts do shrink and grow with the change in temperature from machining. In my experience the shrink about .002 on the diameter from hot off the machine to ambient.

Chip control will be the only problem, use super high feeds and air blasts to clear the chip. Also the cabinet air will make your eyes burn similar to chopping an onion due to the acetic acid that is off gassing from the machined parts.

[MadMax]

It's good to know that delrin runs well in a swiss machine. In my experience, delrin does not absorb very much water. Nylon is pretty bad for water absorbtion and resultant swell, but delrin is pretty stable in that respect. It's interesting that you've seen the thermal expansion issue. If you're machining hot enough to form formaldehyde, then you're close to the melting temperature of the material. Crystalline plastics like delrin will exhibit substantial expansion close to their melt temps.

If you're forming formaldehyde in your machining processes, you need to have good ventilation for your machine. Formaldehyde is a pretty nasty compound. It's toxic and carcinogenic.

Thanks for sharing your delrin experience danrudolph. Could you give me an idea of how long it takes you to do a diameter changeover on your swiss machine? I'm looking at Citizen lathes right now. I hope they're not annoying to swap barstock diameters.

[underthetire]

A lot of the newer swiss stuff can run coolant FYI.

[danrudolph]

Hmm, thanks for the heads up on the chemistry there. I wasn't aware the released compound was formaldehyde. Good to know.

For the job we have, the goal was to push the machine and process to the max to achieve the lowest possible part cost. I am turning at .005"/rev at 8000RPM, very fast. I'm sure you'll have more thermal stability if you take your time. Our tolerances were not super tight, except for a .036" hole .5" deep which was +.0005/-0 which we held no problem.

For setups, you have headstock collet, guidebushing and sub collet. The collet changeover is about 5 mins each, depending if you use the supplied chip guard in place. The guidebushing takes 10 minutes, including setting the tension on the stock. The bar loader takes probably about 15 minutes to adjust. We do not have to swap the channel liners for our barfeed, just adjust the magazine stops, lifter and barfeed collet. I usually do the machine changeover while another guy assists doing the barfeed setup. Not knowing your jobs, stocking the largest dia and turning down may be an option if you want to avoid GB/Collet/Barfeed changeovers.

FYI, we have a Citizen A20 Type 7, very nice machine. Capable of pretty amazing things with some creativity.

[MadMax]

Thanks for your help guys!

Currently I run a very wide range of part diameters from 0.125" to 1.750" parts in steel, aluminum, brass, and delrin which is a bit of a bugger for me, but currently I've only got one machine which can be very taxing on downtime. Having a pair of machines optimized for certain diameter ranges would help me, especially since many of my parts are not very optimally done in a fixed headstock machine so I'm especially keen on looking at a swiss lathe which I can leave a fairly universal toolset touched in.

I've never seen swiss turning up close. Am I correct in understanding that the chip guard is a round throughbored part which covers the face of the headstock collet? I'm guessing it's meant to stop chips from driving back into the headstock collet.

What are channel liners? Are they liners which support long bar? Is it possible to spin 12' bar on a a channel liner at 8krpm without it whipping out of control? So far all of my bar work has been done with 4' bars which are completely enclosed in a spindle liner. I had thought that very long bar had to be run in a hydrobar feeder.

I'm not too averse to a 1hr changeover between parts. We're doing a lot of mid part pull tricks with our current fixed headstock lathe to deal with part stiffness problems. It adds a lot of toolchanging and some concentricity problems so spending a bit more time in machine setup for a comparatively blazing fast runtime is a pretty good tradeoff.

Do you ever run unground stock? I've been trying to find out more about Citizens adaptive guide bushing, but it's hard to figure out what models they're made for. Does anyone here run one?

[UK-Engineer]

What are channel liners?

Depending on your barfeed make channel liners are usually plastic or rubberised guides in the barfeed to support the bar and bar pusher during the machining cycle. Some barfeeds require you to change them in line with the size of the bar you run whereas others use a bigger channel to avoid having to change between jobs. Here in the UK for example on 32mm capcity machines we run a 36mm bore channel and only really change it when bar is below about 8mm. We just limit rpm to stop bar vibrating too much. Plastic is different , especially material like PTFE which in small sizes is like spaghetti. We tend to recommend running as large a bar as you can and just machine down to size as most plastics are relatively straightforward to machine. Failing that you have to optimise channel set for bar size and a channel set can be quite expensive

Do you ever run unground stock?

I'd say majority of users in UK won't pay for ground stock and rely on commercial quality drawn bar. Ground stock is undoubtedly better though and often a prerequisite for very high accuracy (sub 0.010mm) /concentricity parts

I've been trying to find out more about Citizens adaptive guide bushing, but it's hard to figure out what models they're made for. Does anyone here run one?

http://www.cma-citizen.com/Cool_Blaster_AGB.htm

They're available for most of the new machine range from Citizen. They're a nice piece of kit - well engineered and thought out. If you were running a lot of titanium and aluminium (which normally are notorious for size fluctuation throughout a batch) I'd say give it a try but as it can be retrofitted at a later date, you may initially want to try a conventional guide bush equipped machine

good luck

[hacdlux]

I've never seen swiss turning up close. Am I correct in understanding that the chip guard is a round throughbored part which covers the face of the headstock collet? I'm guessing it's meant to stop chips from driving back into the headstock collet.


the defining part of a swiss lathes is the guide bushing you mention above
this is also the biggest learning curve, think of it as a steady rest your cutting tool is only .050 away from the support. allowin you to achieve high l:d ratios

the problem with unground stock is the variation in diameter of the bar which will either jam the bar in the gb or the bar will tumble in side of it

ive ran delrin and nylon in my tsugami with good results biggest challenge i had was getting the bar into the feeder. a .250 piece of nylon doesnt weigh enough to get into the guide chanel of the bar feeder if it gets stuck in the oil.

[DCogswell]

How long are the parts that you want to run on the Swiss-type? Also, do you need to do any cross milling/drilling or any other live-tool operations?

[hacdlux]

so mr. cogswell , trying your hand at online apps work now

[DCogswell]

Originally Posted by hacdlux so mr. cogswell , trying your hand at online apps work now

Recently found this site...who's this?

[hacdlux]

corey