Cast Iron worse than MDF?

[Malcolm Wheeler]

I am buying a table saw extension router table and one of the vendors who has been in the game for a long time stated that I should never, ever, ever, ever think of getting a cast iron wing extension, and that I should solely focus on formica covered MDF. He said that as long as you keep it dry, MDF will stay dead flat for years and years, but that cast iron anything will always twist slightly as the casting pressures are released.

As I said he has been in the game a while, but he nonetheless is a vendor, so I wanted to turn to the Creek community to see what other opinions there are out there. Any comments?

[David DeCristoforo]

???????????
Who is this guy? He is selling, I presume, PL covered MDF router table tops? Of course he is correct. That's why almost every woodworking machine ever built has an MDF top....

[John Schreiber]

Based on that, why would it be that cast iron has been the highest standard since . . . I don't know when?

[Aaron Black]

I guess I can see some sorta point there, I just think different materials for different applications. As far as cast iron on my tablesaw the extra weight helps then there's the sturdyness factor I've never seen personally a cast iron top move enough to worry about, but i still check mine every spring. The little movement you might get might be from the main part of table moving to parts made of the same material usually move together thats why you will see cast iron motors with cast iron heads otherwise until about 98 youy would have head gasget problems. Before you take my advice to stick with cast iron, you should know i think the people on here that make sure their machines are so "on" that you can balance coins on end or whatever are either a little goofy or have wwwaaayyyy to much time on their hands. no offence ment to anyone. But even high end production shops don't spec their machines like that I know I've fixed alot of their machines. HAPPY SAWDUST

[Steve Rozmiarek]

That's complete BS. Temperature variations cause metals to expand and contract. I don't know about you, but I like a pretty narrow range of temperature in my shop, and it does not change much. Different metals expand at different rates, but for cripes sake, you don't work at zero degrees one day, and 120 the next.

[Don C Peterson]

I had to check the calendar to make sure it wasn't April 1st... What a load of horse manure!

[Malcolm Wheeler]

David @5:19 pm - yes indeed he sells tables and does not have a cast iron option in his list of offerings.

[ian maybury]

The problem with cast iron relates to release of stresses locked into it during the casting process. Whether or not its a problem depends on how well the castings have been made (the casting technique matters a lot) and processed afterwards to stress relieve them.

What were called 'green' engine cylinder blocks (something you would think would never move) for example used to be cast and thrown out in the back yard for a year or so before machining so that natural temperature cycling would result in their stabilising after whatever warping first took place.

Machining blocks that were too fresh would result in often serious movement - for example cylinder bores out of the vertical. Nowadays the heat cycling is done in a more controlled way in ovens, but even so it's probably skimped on cheaply sourced castings.

When you're looking to achieve flatness tolerances within say 0.003 in over the thin casting that is a machine table (which probably invites premature cooling of parts of the piece during pouring, and hence stress inclusion) this must be a big issue.

That said you'd have to think that MDF whether laminated or not must be susceptible to considerable movement if atmospheric moisture gets into it. Perhaps it's pretty stable with an impervious laminate and sealed edges...

[Cliff Rohrabacher]

He is right Cast Iron is for losers and amateurs who don't know what they are doing. I'll take particle board any day over mere metal.

The last couple weeks there have been a flurry of posts about sales-creep's representations that simply boggle the mind

Recently one of them was Grizzly bearings all burn up in a matter of months

It begs the question: "How many kinds of stupid do they think the customer is?"

[Bill Huber]

Ok, I bought a new Jet contractor saw, it came with stamped steel wings. Not bad but they were not flat. I got some Craftsman webbed cast iron wings and install them, it sure made a difference in the vibration of the saw, still a little but less then the steel.

I then got a chance to get so heavy cast iron wings and remove the webbed ones and install the heavy cast iron ones, What a difference, no vibration at all, it was like a different saw.

So I would say go with the cast iron and in 75 or 80 years you can always pull them off and have them flattened again.

[John Gornall]

I'm very happy with my Lee Valley steel router table - it will never sag. I think it could be built into a table saw extension table.

[Robert Reece]

I am going to somewhat agree with the salesman here.
Quality MDF is manufactured to thickness tolerances of a .005". That's pretty good and about what we expect from a quality cast iron table. If you put a quality plastic laminate on both sides, that table should be essentially equal in flatness to a cast iron table.
And a lot cheaper.
Moisture resistance is a wash to me since cast iron rusts, but MDF swells. Both really need to be kept in a reasonably conditioned shop.

At the end of the day, I think the laminated MDF does exactly what we need from our router tables and doesn't require the expense of a milled cast iron top. If you want a cast iron router table, get a shaper instead.

The only reason I have considered a cast iron router table is so I can use magnetic featherboards. I'm still up in the air about which way to go.

Anybody know a source for a quality cast iron router table top? I called Quality Grinding, but he said he isn't doing router table tops now, maybe in a few months....

[Peter Quinn]

Wow. Wow.Wow Now I have heard it all. "This news just in....MDF found to outperform stress relieved cast iron for wood machine tables, industry struggles to adapt...details at 11PM.."

So , I would have to agree with the sales jerk to the extent that some form of melamine or laminated sheet good is probably more appropriate for a router table top, and definitely good enough. Appropriate from the perspective of cost, ease of modification as the need arises, and the ability of a wood worker to customize it to meet their specific needs. I like router tables to be very flexible (in terms of set up options, not top stiffness), quick to set up, and reasonably accurate, and cast iron is not a prerequisite to meet any of these conditions. But to say that you should "never" use iron for a top because it is unstable? Holy crock of rancid pudding Batman! I would file iron router tables under "ULTIMATE SOLUTION BORDERING ON OVERKILL", but not under BAD IDEA".

Perhaps that moron should come and look at any one of the three shapers presently in my shop, the youngest of which is 15 years old. All are between dead flat and very nearly dead flat. Ever seen a shaper with an MDF top? Ever wonder why not?

[glenn bradley]

Bwaa-ha-ha-ha. Is it April again already???

[Wes Grass]

"cast and thrown out in the back yard for a year or so before machining"

Which does, basically, nothing.

Temperature cycling between hot summer and winter snow does nothing to stress relieve an iron casting. Neither does the mild etching of the surface from rusting in the weather. Both old wives tales, urban legends, or myths, or whatever else you prefer to call them.

Nothing but heating the thing literally red hot and cooling it down over a period of a day or 2 will do anything significant to reduce the internal stresses. And just by coincidence, that costs a lot of money in energy to accomplish, which a lot of companies don't want to spend, which is why castings get thrown in a yard ... which doesn't hurt them any and is the cheapest place to store them while they're waiting to be used.

And so they're never really flat, and don't tend to stay perfectly flat even if you decide to tear the thing apart and send it out to be reground. Every pass the grinder makes relieves a little stress and it warps again.

But worse than MDF? Umm, no.