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zephyr9900
06-29-2009, 04:09 PM
Hi all, my first post here and I have a question.

I've built a small CNC retrofit for my Feeler lathe:
http://www.prototrains.com/feeler/X-Zmech.jpg

I made the structure from aluminum tooling plate. Along with some redesign to accomodate waycovers (I'm just using a thin sheet of rubber stretched around the toolplate for now) I would like to redo the retrofit from steel to gain the stiffness that steel gives vs. aluminum. Is there a steel equivalent of the aluminum tooling plate--i.e. won't warp when I machine it?

I've seen 1144 and 4140 recommended for machine parts, but I've been unable to find out if they will machine warp-free. I don't have grinding or heat-treating facilities available.

Thanks,

Randy

lazlo
06-29-2009, 04:27 PM
Very nice job Randy! I notice that you've added encoders to your steppers -- what controller are you using that does closed-loop stepper control?

Unfortunately, Stressproof and ETD-150 only come in rounds and hex. An alternative would be CPM's Maxel "Tooling Alloy", which is high-temperature stress relieved 4140 Pre Hard (like ETD-15), but it does come in flats:

http://www.crucibleservice.com/steelStore/gradeDetails_flats.cfm?gradeCode=B4141&shape=FL

Peter N
06-29-2009, 04:42 PM
What you want is a nice lump of P20.
Primarily a mould tool steel, it is however pre-toughened (or pre-hardened to you lot over there :D ) and is a good alloy steel that you can machine nicely without having to harden or grind.

There are 3 basic grades of P20 available, a free-machining grade, a premium 'hi-hard' grade, and a low suplhur grade where you need a high polish, as the free machining grade won't give the best mirror polish.

Have a google for P20 Mould (Mold) Steel and you should find what you need.

Peter

Forrest Addy
06-29-2009, 05:03 PM
Cast iron would be my choich. Look you DrraBass in google. They will saw to order but it wont be cheap. Nor will shipping. OTH you will not need to sweat galling ars you do with aluminum to aluminum. It machines nice too.

lazlo
06-29-2009, 05:09 PM
Cast iron would be my choich. Look you DrraBass in google.

<Smacks forehead>! :) Yes, DuraBar or VersaBar (continuously-cast iron) would be better than tool steel: not as strong, but much better vibration damping.

DuraBar sells from local distributors. VersaBar will ship directly from the foundry:

http://www.versa-bar.com/

zephyr9900
06-29-2009, 05:41 PM
Lazlo, Peter and Forrest, thank you for your answers.

Cast iron would have been my first choice based on its damping properties, until I read horror stories about machining it and the fine abrasive swarf/dust that will ruin the ballscrews and ways on my Tormach mill. Is it actually as bad as that? I'm a hobby/garage-shop machinist and would rather not deal with that if it's going to be a problem.

I don't need strength per se--I dented a piece of the aluminum tooling plate the other day when I forgot to put a washer under the head of a 4-40 capscrew I was tightening into it. I just mentioned heat-treating and grinding more from the aspect that I couldn't anneal/normalize stressy steel.

Free-machining P20 sounds promising but I'm downloading datasheets on all the materials mentioned. Almost all my experience is with aluminum and brass.

Lazlo, the steppers came as surplus with the encoders (which I'm not using) already attached. I'm driving the motors with a Xylotex board. Actually, for clearance reasons I'm swapping out the NEMA23's for NEMA17's. The ballscrews have a 1mm pitch so I really don't need to worry about motor torque. :)

Forrest, I don't have any aluminum-aluminum sliding. Both axes have a THK ballscrew actuator and 10mm Thompson linear bearing in parallel.

Randy

lazlo
06-29-2009, 06:01 PM
Cast iron would have been my first choice based on its damping properties, until I read horror stories about machining it and the fine abrasive swarf/dust that will ruin the ballscrews and ways on my Tormach mill. Is it actually as bad as that?

I machine DuraBar and VersaBar all the time, and while it is messy: it creates a fine granular dust and you'll get coal-miner hands and face, I just vacuum it up and clean and re-oil after each job. It's certainly not nearly as bad as using a toolpost grinder...

Forrest Addy
06-29-2009, 06:33 PM
If you'e concerned about dust, locate a vacuum pick-up near the tool but you do need good flow for optimum capture. Use a fresh filter or drywass bag. You need the ggood flow. Most home shop vacs begin to clog within a few minutes of start up because of the cheap low arae filters they come equipped with. While they may be emptied often the filter is often neglected.

Evan
06-29-2009, 06:44 PM
Nice work Randy. There is something you can easily do without much work that will give you much of the advantage of iron without having to rebuild the entire attachment. Your design is perfectly suited. It is entirely possible to combine iron with aluminum even though they have very different coefficients of thermal expansion. It must be done so that the differential forces are always in balance.

In your case you can buy some square steel key stock in a size the same thickness as your tooling plate. By drilling evenly spaced and centred holes along each edge the key stock may be fastened along each edge on each table. If all fasteners and the holes for same as well as the material itself mirrors the piece on the other side the expansion forces will balance and no warping will occur. Most shops don't change temperature very quickly or much anyway.

Doing this will not only provide some of the stiffness of steel but it will also dramatically change the resonance qualities. Because of the very different moduli of the materials and because of being laminated they will together have better damping than either would have alone.

Laminating materials will provide more damping than any single material possesses by itself. That why you never see laminated bells... :rolleyes:

websterz
06-29-2009, 10:40 PM
Where are you located? Lots of folks on here have surface grinders...:)

zephyr9900
06-30-2009, 05:37 AM
Sorry, websterz, I've now filled in my profile a little. I'm just south of Sacramento, CA.

Forrest, I should buy a new filter for my shopvac. I've just gotten in the habit of brushing the crud out the pleats with a bristle brush whenever I empty the tank.

lazlo, granular I can deal with. Powdery is what I was afraid of.

I used to have this pop-bead hose on my Tormach's head--I machined a PVC slip-to-thread fitting to take the end of a 1-1/4" shopvac hose. I used it when machining acrylic, but removed it when I built the full enclosure and started using flood coolant full time, but maybe should put it back on if I cut CI.
http://www.prototrains.com/tormach/vac-hose.jpg

Evan, thank you for your recommendation, but I need to make new plates with different thickness anyway to accomodate the waycovers I'm going to incorporate. If not for that I'd seriously consider doing what you suggest.

Randy

Evan
06-30-2009, 08:32 AM
It wasn't explicity mentioned that cast iron is cut dry with no lubricant or coolant. This makes the cleanup easier but it still makes a real mess. As suggested, a powerful shop vac with a velocity nozzle attached right beside the cutter will minimize the issue a lot. Another way to control the dust is to use magnets.

Here is an example when grinding end mills:

http://metalshopborealis.ca/pics3/tcgrind1.jpg

John Stevenson
06-30-2009, 08:59 AM
Randy, really neat application and I did say a few months ago when you posted on the other site that i was suprised than more people hadn't copied the idea.

Audit in the UK did one many years ago that bolted to standard Colchesters and old Turret lathes to give them a CNC capability that wasn't affordable at the time.

Recently been a thread on here on the Audit attachment.

.

Cheeseking
06-30-2009, 11:15 AM
Randy,

I've used something called "Fremax" /"Freemax" plate. Sp? I think it's a trade name for a free machining plate steel. We used it for stripper plates and for parts where large chunks of stock needed removal but we couldn't have distortion. Cuts really nice.
Here's a link I found http://www.cintool.com/catalog/Low_Carbon/FM15.pdf
Hope this helps.

Paul

zephyr9900
07-02-2009, 08:15 PM
Evan, thanks, I did know that CI is supposed to be machined dry. If I ever go there, maybe a ring magnet stuck on the pop-hose vacuum nozzle? The only CI machining I've ever done was to add a second drain to my Tormach's table. I wish I knew about the magnet trick back then--that's where most of my aversion to CI comes from. Really fine dust rather than granular chips.

John, I looked up the Audit thread. I had been wondering why not just arrange it as a tooling plate and dispense with the turret, but I now realize that it is arranged that way (slant-bed style) to not restrict the workpiece diameter vs. swing over the carriage. Neat arrangement.

Paul, thank you for that lead. Fremax 15 looks very promising, and I hadn't heard of it before. I see that it is used by Jergens for fixture plates too. I think that, based on my limited experience with machining CI, that I will go with the Fremax 15 unless it is very expensive in offcuts.

Randy