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.

[Gary Herrmann]

I'd suggest buying from someone else.

[Steve Rozmiarek]

"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.


Had a Caterpillar engineer tell me this too. Extension tables ain't engine blocks either. .005" out on an engine is devastating, and completely inconsequential on a table saw.

[Wes Grass]

And I've heard the best block to build a race engine from is one that was parked in the garage when the house burned to the ground. And it didn't get hot enough unless the aluminum intake manifold melted away.

But that seems a bit extreme just to gain an extra HP or 2 ;-)

[Jim Summers]

How thick? I just finished getting the sag out of a router table top that is a laminate of .75" mdf and .75" plywood. I think cast iron would never have given me the problem.

HTH

[george wilson]

Get cast iron. Mine have been flat since 1964. That was total B.S..

[Glen Dickey]

Haha. That salesman is wrong. Cast iron is what they build machine tools out of. WAY more accurate than any woodworking stuff. Yeah, cast iron can warp, but so dose MDF. Heck, just get it wet and put some pressure on it. Cast iron is very strong, but it can move, but its pretty rare its ever serious for most woodworking machines. I am a machinist by trade, and just about every table or way is either cast iron or steel on machinery. And the tollerances for machine tools is a LOT tighter than woodworking equipment.
MDF is great for shop built stuff, and its stable under the right conditions.
The reason they are making all the tables out of MDF is because its cheap, and light. Cast iron is expensive, heavy, and you must machine it after its cast.
For something portable (like a router table) MDF is fine. My router table is made out of it. If I had the option, Id take cast iron any day.
Some of my old Oliver machines are from the 1920's, solid cast iron, flat as can be, and running just as well as when they were new.

[george wilson]

I would avoid that dealer. He's either ignorant,or trying to con you. Both,you could do without.

[Barry Richardson]

All the MDF router table tops, that I have expreienced, sagged over time with the weight of the router. We have a solid phenolic top at work, It stays perfectly flat but kind of $$$

[Rod Sheridan]

If someone were interested they could perform the following two searches on this forum;

1) "Help! My router table is sagging"

2) "Help! My shaper table is sagging"

That should provide enough data for an un-controlled yet informative study.......Rod.

[Cody Colston]

Evidently this sort of bs is the in-vogue sales technique...diss a competitor's product in an attempt to make your own look better.

Just like the doofus who said all Grizzly bearings would fail in a few months, the router top salesman would have been better off just touting his product instead of attempting to trash another.

Laminated MDF is perfectly suitable for a router table top. I would wager that is what a large percentage of us here are currently using. But, it is not more stable than cast iron.

The snake-oil salesman would have been better served by touting MDF as an acceptable, lower priced alternative to cast iron rather than trying to claim it was more stable.

[Tom Clark FL]

Hmmmm! Let's see. The cast iron tables in my shop include the table saw, band saw, planer, shaper, and joiner.

The most warped pieces of crap in the shop are all made with MDF.

I build all my shop cabinets with good plywood, some laminated, some not.

The biggest warped item is a 3x6 table made from laminated MDF. It took three pieces of heavy angle iron bolted under it to keep it from warping farther!!! Lay anything round on the table and it rolls right to the middle…

[ian maybury]

Errrrmmm. So has anybody (apart from the salesman) said an MDF table is better than a cast iron one? Or that the reverse is true in all circumstances?

It's very clear that cast iron that's not been carefully cast or treated may be problematical, but that cast iron has other advantages like toughness and vibration damping too. On the other hand it also seems pretty clear that a well made MDF and laminate table can do a very good job, and has it's own advantages relating to cost, ease of modification, weight and so on.

I'd say it's a pays your money and takes your pick sort of issue based on trading off between your priorities....


On use of magnets to hold stuff down. Just conjecture, but how about laminating some light gauge sheet metal over MDF so you can use magnetic fixtures? You'd probably need it on both sides to eliminate differential expansion, but you could also laminate on top to eliminate rusting and improve sliding...

[Wes Grass]

Anything you put between the metal and the magnet will reduce the magnet's hold. So the laminate would have to be really thin. Like, *really* thin. Even a 32nd thick is probably too much.

[Leigh Betsch]

I'm willing to go out on a limb here and say MDF is better. Better at floating that is.

[Kyle Iwamoto]

Umm, just to be the devils advocate, the OP did state that he was selling EXTENSION WINGS. Not the table, or table wings. My extension wings are MDF. I would agree, that EXTENSION WINGS made of cast iron would not be PRACTICAL, would make my saw be 1000 pounds instead of 700. Would require an additional set of legs to my wing legs. I would have to say that I prefer MDF EXTENSION WINGS. The cast iron extension wing would probably sag the entire saw as well as my fence rails. Off the top of my head I would say that the extension wing is as big as the rest of the saw. It would be hard to support if it were cast.

I would agree that the table and wings are to be made of cast iron.

No, it's not April.

[Bill White]

Oh well......Anyone wanna buy a CI TS top?
Bill :p

[Ken Garlock]

Mechanical Engineers,
Civil Engineers,
Professional Machinists,
Stand-up and identify yourselves, so that we can clear the grain from chaff using facts. Electrical engineers need not apply.:eek:

I have heard so much pelosi regarding MDF and CI that I have to laugh. So, I went out to the shop and measured the bowing on my Woodpecker MDF top that has supported my PRL for the past 5 years. I used my Starrett 36" straight edge, and found that my table had a depression of at least 14 thousandths across the long dimension. This is notable since the MDF is backed by two pieces of angle iron in both directions. Without looking, I think the angle iron is 1/16 thick with 1" web. It is attached with wood screws to the MDF. Am I worried, not in the least. Would a Cast Iron top be better, I think so.

[JohnT Fitzgerald]

Electrical engineers need not apply

Hmph.....THAT was uncalled for..... :)

[John Harden]

....
I have heard so much pelosi regarding MDF and CI that I have to laugh...

Now, THATS funny!!!!!!!:D

[ian maybury]

Mech eng here! That said the story on 'green' castings in the back yard came from my metallurgy lecturer back in the 80s, so heaven knows what the reality is...

[Wes Grass]

Mechanical designer (no degree), semi reformed ex toolmaker and machinist. Machining is mostly a hobby these days, but my shop contains a 4 axis CNC machining center, as well as a nice Italian toolroom lathe and a manual milling machine. I also own a copy of Solidworks and Surfcam. So I've at least put a big chunk of money into it. My Felder stuff was cheap by comparison ;-) And I sure wish they still made their extension tables from CI.

The stress relief info came from a Naval Research Lab document, BTW. NRL Report M-3296, 'Stress relief of gray cast iron', 1948.

Don't have a link to it, just a copy I downloaded, but it should be fairly easy to find if anybody actually cares to read it.

[John Gornall]

Mechanical Engineer - making a point about router tables that aren't flat.

If the table sags the depth of cut will be correct as the end of the work piece engages the cutter but will be shallow when the workpiece bridges the table and back to the correct depth as the back end clears the cutter.

If a table is crowned in the middle and the workpiece is held in contact with the table at the cutter throughout the cut the depth will be correct the full length.

My table is steel, not cast iron or MDF and is crowned about 5 thou with the router hanging - works well.