Heavy Metal - cutting cast iron table saw top

[Bruce Seidner]

What is the best practice for cutting a hole in a cast iron table saw top. I happened onto a marginal old Craftsman table saw that I picked up cheap and have dissembled the unit and want to cut out the top for a router plate. It matches my working Craftsman contractor saw at 27" and I thought that with all these sagging router tables being discussed there would be little chance of a cast iron top sagging.

My first thought is to use my jig saw with a metal specific blade and then use a file to the template line. My second thought is to use a router with an appropriate spiral bit. I'll start looking around for bits but imagine that the speed of a wood working router is a bit fast for metal. I Googled routing metal and did not come up with much at all.

As always, comments and suggestions are appreciated.

Bruce

[Brian Cosgrove]

I would put a cut-off wheel (6-7") in an angle grinder and cut it that way. I cut metal that way frequently. The router is an accident waiting to happen. Good luck, Brian

By the way, if you don't have an angle grinder, Harbor Freight Tools has a 7" for $39 right now, which is good for a few uses.

[Dave MacArthur]

My Dad did this on his craftsman contractor saw, he just took the wing off and took it to a machine shop, they cut the hole, cleaned it up, and tapped some bolt holes for the router all for $30, well worth it IMHO.

[John Fabre]

I think the machine shop is the best way to go too.

[Bruce Seidner]

I thought a grinder was a type of sandwich. I truly like the idea of getting a shop to do it and will call around tomorrow.

The grinder's look like they can use a number of wheels which is cool. But how do you control what looks like a Dremel on steroids? Is there some kind of jig or attachment that keeps it square to the material. I have a Dremel and there are some nifty attachments for it. I have done some serious damage using it free hand.

[John Fabre]

You might burn up a Dremel, HD or Lowes will rent a grinder, if it doesn't work, you can always take it to a machine shop.

[Scott T Smith]

Using a vertical mill in a machine shop would be best.

Options for doing it yourself - lay it out and drill corner holes (slightly inside of where you want the final dimensions to be). Cut between the holes with a jigsaw, leving 1/8" or so. Build a template for a rounter, and use a carbide or HSS spiral cut bit to clean up the edges.

Cast iron is soft and mills easily. I have a vertical mill, but would not hesitate to use the drilling and router routine if I didn't.

[Bruce Seidner]

Using a vertical mill in a machine shop would be best.

Options for doing it yourself - lay it out and drill corner holes (slightly inside of where you want the final dimensions to be). Cut between the holes with a jigsaw, leving 1/8" or so. Build a template for a rounter, and use a carbide or HSS spiral cut bit to clean up the edges.

Cast iron is soft and mills easily. I have a vertical mill, but would not hesitate to use the drilling and router routine if I didn't.

I know from experience that cast iron cuts easily. I have several cuts made by an errant saw using my cast iron table saw wings as an ad hoc saw horse.

I was unable to find information on routing cast iron. Milling machines are even slower than shapers. A router sounds like a humming bird by comparison. I too was thinking that an HSS spiral cut bit would clean up the edges using a template.

But this was just my theory, hence this post. Have you actually used a router and a spiral cut bit to cut thin cast iron? Is the speed of the router going to be a problem? I can get a cheap voltage controller to further slow it down if my lowest setting is still too fast.

[Mike Seals]

My vote it the machine shop. They'll get the hole perfect for you.

Grinder would work but your holes will not be as clean and a grinder will jump around on you.

[Jim Rimmer]

I had a C'man TS that I made into a RT. Got a friend who had a home machine shop to do it. One thing you have to look at is the webbing underneath the table. Mine was not solid everywhere. We started with the existing opening for the blade and just made it bigger. It does make a great router table but I'm a little concerned about longevity. There a some areas where there is not much material and I'm worried the vibration will eventually win out. I also have a T2 fence on it. I also remounted one of the wings on the back of the table (after the pics were taken) so I have more outfeed support but I need to get a relief slot machined in the wing for the miter gage bar.

If you can get a machine shop to do it cheaply, it's worth a try. Good luck.
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[Mark Woodmark]

Cast Iron is a tough one. You can drill it. I would be afraid to try to rout it. What type bit do you have that will cut cast? I know aluminum can be routed with a wood router and a carbide bit if you dont mind light weight aluminum flakes everywhere on you and your shop. Cast cracks easy and cutting it with heat produces a lot of slag

[Ray McCullie]

One thing to keep in mind is when you drill metal you want to lower you're speed. A drill may get 2700rpm at top speed say. A router may do 30,000 rpm. WAY too fast. Set you're drill press for a low rpm and take small bites so you don't overheat the bit.

Clean up the edges with a sander or file.

That's my two cents, worth every penny...

[Marty Paulus]

I would think any bi-metal hole saw would work. Orange Borg Bi-Metal hole saws say they will cut into Stainless Steel. If they will cut Stainless they will cut cast. Just be sure to use a lube/coolant. Some people use kerosene others will use WD-40. Get a good center punch and drill a pilot hole first before chasing the hole with the pilot bit in the hole saw.

From there I would just get a good file to clean up the hole. A router, as mentioned, would just make a mess and I am sure would screw up the bit. Tapping the mounting holes is no bid deal either. Again slow and lube/coolant.

[John Coloccia]

Machine shop is the way to go. Even if you cut it out with a jigsaw, you still need to make the rabbet for the ledge the plate will sit on. I could toss that on a mill and be done in 10 or 15 minutes. The shop you take it to will probably toss it in their CNC machine and just jog it by hand. Square holes are a piece of cake.

If you want to get fancy, bring the router insert in with you when you go there. They'll match up the cutter with the radius of the corner on the insert for a nice fit. I'd probably ask them to give you about .010" clearance on all sides (that's about 2 or 3 sheets of typical paper).

[Scott T Smith]

I know from experience that cast iron cuts easily. I have several cuts made by an errant saw using my cast iron table saw wings as an ad hoc saw horse.

I was unable to find information on routing cast iron. Milling machines are even slower than shapers. A router sounds like a humming bird by comparison. I too was thinking that an HSS spiral cut bit would clean up the edges using a template.

But this was just my theory, hence this post. Have you actually used a router and a spiral cut bit to cut thin cast iron? Is the speed of the router going to be a problem? I can get a cheap voltage controller to further slow it down if my lowest setting is still too fast.

Bruce, before I bought my vertical mill I cut both CI and aluminum with a router, and yes you need to slow the bit down. If you have a variable speed router, then no problem.

Take your time, make shallow cuts, and you should not need a lubricant. The router does not need to be as slow as a drill, but still fairly slow - maybe around 1000 rpm or so. Feed the router very slowly.

You can do a series of shallow plunge cuts from the top, or make a shallow but full depth cut from the side. The last time that I did this I removed about .030 at a whack via a plunge cut method, using an end mill that would chuck directly into the router collett. The end mill was around .250 diameter as I recall.

[Bo McCorkle]

I happen to be a machinist. The way I'd do it without going to a shop is to center punch the center of your hole then use a hole saw o the appropriate diameter. Or center punch then drill thru with the biggest bit you have an use a die grinder and a burr bit to go out to template diameter. Routers spin way too fast to cut metal. Most routers spin about 20-25000 rpm and most of te time an end mill in cast won't spin more than 1500 rmp or so.

[John Coloccia]

Just FYI: if I understand correctly, he needs to make a square hole with a ledge to mount a router plate. This brings up a good point, tough. Maybe it's sufficient to make a hole for the bit to pass through, and then just mount the router directly to the top with some countersunk screws (depending how thick the top is).

[Bo McCorkle]

I happen to be a machinist. The way I'd do it without going to a shop is to center punch the center of your hole then use a hole saw o the appropriate diameter. Or center punch then drill thru with the biggest bit you have an use a die grinder and a burr bit to go out to template diameter. Routers spin way too fast to cut metal. Most routers spin about 20-25000 rpm and most of te time an end mill in cast won't spin more than 1500 rmp or so.

[Joe Jensen]

Why not try to go the other way. Instead of trying to make a giant hole for the router plate and lift, why not fill in the original throat hole and mount the lift to the base of the cast iron. Note: I don't have a lift, but I am assuming you can raise the router enough to change bits without removing the plate?

[Bruce Seidner]

There was a hardware store I loved to hang out in on my way home from Jr. High. It was small by todays standards but it had hundreds of little bins with different fasteners, drill bits, odds and ends. This may sound too nostalgic and Norman Rockwell but the best part was listening in on the advise and debates that would go on between the owner and the tradesman that would do business there. With everyones able input and experience that memory came bubbling up.

Because I lucked into a almost new Bench Dog ProLift plate I felt providence wanted to have it on a proper table. I then fell into this cast iron TS table that is not as well made or thick as my contractor saw table so routing a ledge will not be in the offing. I am going to call around to some machine shops and have them enlarge the existing blade hole. There are a number of strengthening support ridges under this table where it is taped for the saw arbor and the saw cabinet. I am going to have to use these and maybe tap elsewhere in addition to create the supporting ledges that the router plate will sit on and be flush with the table. This is similar to the design in this months Fine Woodworking where they dispense with the routed ledge and use supports mounted/screwed in as a support ledge with the full cut opening for the router plate.

Oriented like this my TS fence will not be of much use but I will have plenty of miter T-slot to use for a router fence support. My main interest and intent for the router is for long strips for kayak building or spars for boat building. So orienting this to the front of the table saw/router combined cabinet will give me 5' of support before I go to off table support.

But I have learned enough here to think that I should hand this off to a machinist who is set up to do this safely and get it right the first time.

[Troy Turner]

I'd go with the machine shop. They have the tools to do it right..the first time :)

[Bo McCorkle]

I hate this I really wish you were local and I'd just grab that thing and take it to work and throw it up on a bridgeport for ya. Maybe a 20 min job with indicating the table square for the new line up...

[Bruce Seidner]

There are just some things that Facebook, Twitter, and Sawmill Creek can not accomplish. But I do very much appreciate the offers and camaraderie.

I am calling machine shops and will figure out how I want this router plate oriented. It is a piece of cake to fill the cut out for the saw blade by making a totally zero plate. No blade through, just solid.

But using the miter slots for feather boards and fence anchors is something that I might be considering. All things being equal, and this table being on the surgery table, I can likely put whatever holes, slots, etc. where I want.

Tabula Rasa, blank slate. And on the 7th day I will rest.