Machining cast iron on TM-1...good or bad?

[jwknow]

I work with a young engineer that wants to machine "Grey Iron Castings" on our TM-1 mill. I explained to him that the "dust" created from machining this would find its way into the ball screws of the machine. Also, since it is lubricated with grease, that in time, could turn the grease into "lapping compound" and could cause premature wear on the mill. I advised against it but he chose to ignore my advise. Are my concerns valid? Any thoughts on this?

Thanks
JW

[Donkey Hotey]

Who does the machine belong to? Who pays for it when it wears out or breaks down? Are the iron castings a big earner? If the customer is paying enough money, wear that sucker out. If it's a tight-margin job, I wouldn't put that trash in any machine I owned.

I turned a couple of brake rotors on my old manual lathe. I laid wet towels across the ways to catch everything. It was a mess. I'd try to do something similar to the mill if it's a one-time job that absolutely needs to get done.

Don't forget that the machine also runs on linear guides. Those are going to get ground up too. Imagine what it'll do to the coolant pump. The list goes on and on.

[dertsap]

i wouldn t worry too much about it most machines face far worse in a day and keep running strong ,you would need to be running a lot of castings for a large period of time to notice any wear , probably years , an oil skimmer will catch much of the stuff floating around in the tank if there is anything floating
if you can run enough cast thru that machine to wear it out you will have made enough money from that machine to rebuild the old worn machine or let it retire
we currently have a lathe had been running a large cast job for most of it's life (7yrs) ,
it has paid for itself so many times over it is rediculous ,we recently changed a set of slides and a ballscrew on it , small price to pay for the money it generated , most of the wear was due to the fact it never stopped , some of it was due to running cast and the fine powder it produces, if it ran harder materials for the same period of time , the wear and damage would have been far greater

[Geof]

Worry more about the wear on your lungs inhaling that dust. Make sure you use a good face mask and push for a dust collector system on the machine.

[jayhawklawrence]

I agree with the previous posts. Cast iron is what it is. You should expect more wear on any machine. The guys who specialize in machining cast iron take this into consideration and schedule more time for maintenance, keeping the coolant clean, etc. An extra filter system is sometimes justified.

Whenever someone wants to machine cast iron, I would recommend an additional filter type coolant system. However, the cost is not really justified on the TM-1 since the base price starts at $ 22K.

Just keep it as clean as possible and expect slightly more maintenance with cast iron. It is the same with any machine out there.

[Geof]

Have you, or your engineer, ever machined cast iron before? The name Grey Cast Iron is a bit nebulous because it can cover quite a range of properties. Try to tie him down a bit tighter because some cast irons can be extremely hard and quite difficult to machine, others are almost like machining cheese, and are great to work with except for the dust. You certainly need to use the correct grade of carbide and if you look at recommended speeds you will probably find they seem slow; a good way to burn the end off even carbide tools is to try and push the speed too high. Feeds on cast iron can often be very high, maybe two to five times what you would use on steel unless you need to go slower for a good finish; but not too slow because you can glaze the surface. Tools should be zero top rake or negative rake and if you use HSS drills it is a good idea sometimes to grind the cutting edge flat to remove the rake from the helix angle; alternatively, never use a pilot drill because you can get serious grabbing with a regular drill, having the center contact at the web stabilizes things. Cutting fluid/Coolant is normally not required for cast iron but it does help combat the dust problem, at the price of creating a grinding paste in the coolant tank. Personally I think good dust collection and face mask are preferable; just standing there holding the nozzle of a good shop vac near the tool can be very effective. And on the topic of dust it is a good idea to have a complete change of clothing at work if possible, and shower before going home; the dust is insidious and if you have nice light colored carpets and furniture and work a lot with cast iron you can find things getting grey marks.

[jayhawklawrence]

Great information Geof and very useful. I think the point here in my mind was whether the TM-1 was inherently not good for cast iron. My point is that any of the standard CNC Verticals have the same issues with cast iron. Whether it is linear guides or box ways you are still going to have issues you don't have with other materials when the slurry is basically a grinding compound. I imagine I have been in over a thousand plants that machine cast iron including my own. Yes, I know what it is but thanks for very good information.

[PBMW]

Just say no.
hard to do if it ain't you machine.
I had a customer that had me turn some FR4 into bushings. Nasty Nasty stuff. Took a day and a half to clean the machine. I charged the customer for it too. Never again. Crap jobs like that are just that...crap jobs

[Geof]

Originally Posted by PBMW .... Crap jobs like that are just that...crap jobs

But somebody gotta do em .

I had a job for a year as a toolmaker in the machine shop for an iron foundry that made cast iron fire hydrants and all the cast iron fittings for water mains. Talk about dirty, crap jobs. The foundry looked like some of the scenes from Lord of The Rings and the machine shop could have stood in for the Black Hole of Calcutta.

[jwknow]

Maybe I should clarify my situation....I work in a "maintenance machine shop" in a grey iron foundry. The work I do is in-plant machine repair. When equipment wears out inside the foundry, i.e.....bearing shafts, rollers, etc., I make new. The actual castings we make are all machined at an outside source so we never really machine any cast iron in plant. I just make various parts and spare parts in our in-house machine shop that keeps all the equipment inside the foundry running.

They recently bought us a TM-1 mill, mainly at my request, for our shop. Its the only piece of CNC equipment in the shop. Everything else is manual...mills, lathes, grinders, etc. The original intention was just to make general parts and spare parts on the TM-1.

The grey iron castings I was referring to in my original post have a "sticker" in them. Its an area in the casting about 1" by 2" that now has iron in it that should have been a pocket. Just a little problem during the molding/pouring process. Normally they would just scrap these castings and remelt them.

Our "young" engineer just took a 4 day Mastercam class and wants to use the TM-1 for machining these "stickers". He really just wants to play around on the mill to see what he can do with his "new" Mastercam skills. There are currently about 50 to 100 parts that need machined. The problem is that once we start using this machine for milling "stickers", that everytime they pour castings with a "sticker" in them they would just bring them to the machine shop instead of remelting them as has always been the practice. The engineer has already admitted to me that it would probably be more cost effective to remelt but he wants to machine them anyway.

I tried to explain to him that we just need to keep the cast iron away from this machine if possible. As I said, this the only piece of CNC epuipment in our shop and I'm doing what I can to keep it in good shape and holding good tolerances.

I honestly was hoping that if I got enough responses from you guys that backed my positions and concerns, I would show them to him and he would rethink his position and scrap his whole idea of prematurely aging this mill.

Thanks for all the responses so far
JW

[Donkey Hotey]

Originally Posted by jwknow The engineer has already admitted to me that it would probably be more cost effective to remelt but he wants to machine them anyway.

There's your answer. Tell him to bring in pieces of lumber to practice with. Tell him to buy scrap aluminum to play with. At about $2/pound, scrap aluminum bar ain't that pricey. It's great that he wants to practice but why do it with such awful material?

OTOH: this might be your opportunity to justify another machine. Maybe it's more 'cost effective' to remelt the parts but that might cause schedule or delivery issues that nobody has considered. If there's a justifiable need to have remachining services in-plant, here's your opportunity to save them in ways they hadn't considered. Maybe they'd start bringing in some of that farmed-out work if they knew they could afford to do it. Maybe there are quality issues that they could reduce or eliminate if they brought that capability in house.

Here's a suggestion to have in your pocket: the VF-2 is available with a graphite machining option. If I understood it correctly, it was a dust collection system and it pressurized all of the way covers to keep abrasives out of the wearable parts.

And of course, this would mean that you'd now have two CNCs at your disposal.

[Geof]

Your clarification makes a lot of difference. No, don't let him near your machine; lock him up. As someone pointed out in an earlier post you don't worry about cast iron being hard on a machine if while you are beating the machine to death you are making more than enough money to buy another one.

But!!!!!!! If you are beating a machine to death doing something that is a losing proposition anyway that is not sensible.