Jet vs. Grizzly

[Dick Strauss]

Tod,
I stated "The more bracing or thicker material used, the lower the frequency." This "bracing" refers to adding webbing to the lathe bed to change the frequency and increase stiffness.

Can't you weld/braze steel to cast with bronze? Speaking of materials development...one of the most specialized and interesting steel materials companies is Dynamic Materials (especially their Explosive Welding Division). This explosive cladding process was originally refined by DuPont back in the 60's and is now coming to the forefront for certain applications.

http://www.dynamicmaterials.com/Divi...0Metal%20Group

Garry,
I think you mis-characterize the advantages of cast iron, especially given that many of these lathe designs were introduced so many years ago. I wouldn't agree that cast iron's properties have been embellished or hyped.

Maybe I'm splitting hairs but (please tune out here if you don't want to read techno-babble) ...I also think the material plays a bigger part than you mention. If it can attenuate better, then it doesn't have to be as massive. The irregular crystaline structure of CI slows and scatters phonons (vibration and sound) within the material due to impedance mismatches at the grain boundaries. This irregular structure tends to attenuate at a given frequency and scatter into other frequencies making the whole structure more capable of shock absorption without transmission. On the other hand... because steel is more regularly organized, it has better (more consistent) phonon transfer at a given frequency (less attenuation) and will transmit the shock better.

Apples to apples...I have 1" thick hardened steel plate (Rc>70) that will ring like a high-pitched bell but I've never found a 1" CI plate of the same size that would ring like that.

[Vaughn McMillan]

...Maybe I'm splitting hairs but (please tune out here if you don't want to read techno-babble) ...I also think the material plays a bigger part than you mention. If it can attenuate better, then it doesn't have to be as massive. The irregular crystaline structure of CI slows and scatters phonons (vibration and sound) within the material due to impedance mismatches at the grain boundaries. This irregular structure tends to attenuate at a given frequency and scatter into other frequencies making the whole structure more capable of shock absorption without transmission. On the other hand... because steel is more regularly organized, it has better (more consistent) phonon transfer at a given frequency (less attenuation) and will transmit the shock better.

Apples to apples...I have 1" thick hardened steel plate (Rc>70) that will ring like a high-pitched bell but I've never found a 1" CI plate of the same size that would ring like that.

Not splitting hairs at all IMHO, Dick. This finally answered the question about what the difference was for me. I know and understand that a steel lathe bed can be fabricated to minimize harmonics, but having a self-damping material helps.

I also think Frank is right about the difference not really being a difference for his intended purposes.

[Stuart Ablett]

Hey Dick, thanks for that, the idea that the composition of the cast iron, compared to rolled steel it so different, could not explain it properly.

I also know that the type of cast iron used in things like lathes is of a different type than used in other things, for example bells, they are, or were mainly cast iron or some other cast metal, and they ring just fine, but the "Gray Cast Iron" used in most tools, does NOT ring like a bell, and the reason is like you state.........

irregular crystaline structure of CI slows and scatters phonons (vibration and sound) within the material due to impedance mismatches at the grain boundaries. This irregular structure tends to attenuate at a given frequency and scatter into other frequencies making the whole structure more capable of shock absorption without transmission.

......... thanks for explaining that, I understood it, but I did not explain it well, or at all.

Cheers!

[Garry Foster]

Tod,
I
Apples to apples...I have 1" thick hardened steel plate (Rc>70) that will ring like a high-pitched bell but I've never found a 1" CI plate of the same size that would ring like that.

Dick
You are right about that but it isn't that tough to stop that ringing..
Also I don't think the lathe on question had hardened steel plate. I believe it was cast not forged steel..Or did I miss something in the discussion? I just thought I have some (to many) old brake rotors sitting outside. I think I'll find time today to hit some with a hammer. From what I am told these are mostly cast steel today. Be interesting to see how bad they ring.

And if anyone wants to play with determining the frequency something resonants at and is tone deaf like me. Use one of the many sound analysis programs for the pc sound card. I used one when I made my wifes wind chime and it worked well on even a cheap laptop mike.

Garry



Ok

I just went out for some work stuff and as I passed my pile of old brake rotors I picked up about eight of them one at a time and tapped them with an old bike handlebar laying close by. The results were not conclusive but none of them rang like the bells of St Mary's. There was a considerable difference and some generated nothing more than a thud while some rang for a very short period of time. Even ones that looked identical showed considerable variation. One thing that was clear is that any that had even a little mud caked on them all generated a thud. This makes me believe even more that if there was any ringing or tendency to vibrate that it would be a simple mater to dampen it out. Not very scientific but pretty informative to me.

[Dick Strauss]

The irregular structure is what sometimes makes CI brittle. The iregular structures acts like built in defects.

Depending on the trace elements, the Grizzly steel bed may or may not need heat treatment/hardening. Higher quality steels have more uniform composition (especially carbon distribution). This is especially true for powdered metals (they want uniform carbide particles throughout the tools). Typically hardening helps to organize the available carbon in the matrix (or adds carbon to the surface in the case of oil hardening or acetylene hardening). Hammering and forming also help to organize the crystaline structure and make it stronger.

You wouldn't want a cold rolled steel bed on your lathe.

I guess if you wanted to try to dampen lathe vibrations you could try some Dynamat (usually used in car interiors for low frequency roadnoise absorption) attached in various places under the ways of the bed.

[Frank Fusco]

Dick, you didn't hijack anything. I had hoped to start a discussion like this. The sharing and learning is what it is all about here. Admittedly, my intentions were selfish. I'm wanting to make a decision that is best for myself. But, if others gain also, super.

[Frank Fusco]

hey frank.....i know you said that you`re changing lathes so you can spin bowls and hollowforms...be sure to factor in the tools-n-chucks necessarry.
the lathe is actually the cheap part

I'm in pretty good shape there. Have a great set of Don Pencil hollowing tools, a PSI mini chuck, and piggy bank is almost ready for a larger chuck. Except for wiring the 220V, I have stacks of wood and am ready to spin.

[M Toupin]

Basically Cast iron is a good, if not great material to use for the cost issue and for most of the strength and durability issues, I mean look at all the 100 year old band saw out there that are still in use, but.... we have moved on.

Stu, I'd have to disagree with you on that point. True for the hobbyist and light industrial stuff, but the high end commercial stuff is another breed. Look and any of the large commercial stuff and you'll find cast iron and lots of it. For example: http://www.northfieldwoodworking.com...chBandsaws.pdf

Nowadays, we can make a much better band saw out of steel.

Dunno about the "much better either"... cheaper is my take. It's much easier and cheaper to weld steel than to cast iron. The costs of GOOD quality foundry and the time required for proper curing would far outweigh any added costs associated with a welded band saw. Designers go with thinner materials for a reason, not because they don't want to "over engineer", but to save costs. The cost is ALWAYS the bottom line in any business. Weather it's to save production costs or to save shipping costs. Just because a given manufacturing method isn't the norm anymore doesn't mean it's inferior, just more expensive than the alternative. As with many things, quality lost out to cost long ago.

Mike

[Stuart Ablett]

..............Ok

I just went out for some work stuff and as I passed my pile of old brake rotors I picked up about eight of them one at a time and tapped them with an old bike handlebar laying close by. The results were not conclusive but none of them rang like the bells of St Mary's. There was a considerable difference and some generated nothing more than a thud while some rang for a very short period of time. Even ones that looked identical showed considerable variation. One thing that was clear is that any that had even a little mud caked on them all generated a thud. This makes me believe even more that if there was any ringing or tendency to vibrate that it would be a simple mater to dampen it out. Not very scientific but pretty informative to me.

Yes the brake drums will ring like bells, but a brake drum is a whole different kind of cast iron than a lathe bed.

[Garry Foster]

Yes the brake drums will ring like bells, but a brake drum is a whole different kind of cast iron than a lathe bed.

Stuart

None of these were drums, All rotors. But as I had stated in an earlier post it is my understanding they are cast steel. And that is what I understood the Griz lathe to be. So apples to apples, cast steel to cast steel so to speak.

Garry