PDA

View Full Version : Cutting 18x18x0.125" 4130 with too-small tools



madwilliamflint
10-19-2011, 03:41 PM
I let excitement get the better of me in accepting my first commissioned job. A buddy of mine is making a guillotine for his Halloween party and wants me to make the blade.

Price is settled and I have material. I also told him that there is a distinct possibility it will be beyond me, but I'll give it everything I've got short of hand-filing the thing.

The end piece is (I don't have the measurements on me) 16" down the long side, 3.5" along the short side, and 15" across.

He does want a bevel on the blade but asked me not to make it razor sharp because some guest will cut their fingers off.

There are also 3 1/4" holes to be drilled equidistant, centered 1" from the top.

Ok. Here's the problem.

I've got a mini-mill, a 7x12 lathe (useless for this in any form I imagine but hey, list your assets) and THIS combination miter saw (http://www.harborfreight.com/12-inch-sliding-compound-miter-saw-with-laser-guide-98194.html).

Last night the happy UPS man delivered my happy 12" abrasive cut-off blades, so I put one on the saw, clamped the steel down and tried to take a test cut off an edge, to see how it would behave.

Now... I'm not sure what I expected. Sparks flew and I drew the blade back and forth over the material with a light hand. My fear was that if I plunged the thing in, that I would shatter the blade and it would dismember me at those rpms.

I only got most of the way through it before realizing that I should probably ask you guys before getting myself killed or the house lit on fire by streaming sparks.

I THINK I can position the thing such that I can take the long (diagonal) cut in a couple passes from each side.

But once I have the roughed shape, I'm not sure what to do with it.I can tilt the miter saw over by 45 degrees and cut/grind a bevel in that way I suppose but in light of last night's escapades, that sounds pretty dangerous.

Ideas?

lynnl
10-19-2011, 03:54 PM
Holy cow! A guillotine for halloween! :D

Every kid'll be wanting one. :)

I'm not sure I'd want to be associated with that one. But you know the situational environment there better than I.

As for the fireworks with the abrasive cutoff blade; yep, that goes with the territory (how do you spell that word - too lazy to look it up). That's why I've only used one two or three times. I'm not sure whether it's best to cut thru in one pass, or go thru with incremental passes. I'm sure someone will shed light on that.

As for putting the bevel on, what do you have in the way of grinding tools? I'd think for the planned purpose, just enough bevel for the visual effect would be adequate. Probably a handheld 4.5" mini grinder would work for that.

RTPBurnsville
10-19-2011, 04:02 PM
I have cut lots of similar material in the past using those blades and a skillsaw. Yep, lots of sparks and grinding dust. I always cut completely through and slowly worked my way to finish the cut.

Robert

madwilliamflint
10-19-2011, 04:03 PM
I have cut lots of similar material in the past using those blades and a skillsaw. Yep, lots of sparks and grinding dust. I always cut completely through and slowly worked my way through the item.

Robert

Hey thanks.

So I shouldn't be put off by the theatrics of it?

How best to deal with the dust w/o a cartridge respirator?

(Got a feeling the answer is going to be "get a cartridge respirator.")

uncle pete
10-19-2011, 04:21 PM
Without normal designed to be used for working sheet metal shears, I've always found making up a layer of plywood, sheet metal and plywood on the other side works well when working with sheet metal. This backs up and provides a rigid assembly. May not be needed with your saw but it works real well when drilling holes. The sheet metal cuts far cleaner, easier doing it that way. Failing that, A quick visit to a local sheet metal shop and they would shear it to size real fast and it's cheap.

Pete

2ManyHobbies
10-19-2011, 04:23 PM
The abrasive blades are surprisingly durable so long as you keep the cut and the blade in the same plane and don't let it start bouncing around. Just give it some elbow and get 'er done.

For the dust on a one-off? Cut it outside. Put a fan at your back if there isn't much of a breeze.

madwilliamflint
10-19-2011, 04:24 PM
Without normal designed to be used for working sheet metal shears, I've always found making up a layer of plywood, sheet metal and plywood on the other side works well when working with sheet metal. This backs up and provides a rigid assembly. May not be needed with your saw but it works real well when drilling holes. The sheet metal cuts far cleaner, easier doing it that way. Failing that, A quick visit to a local sheet metal shop and they would shear it to size real fast and it's cheap.

Pete

Yeah I like that idea. What do you bind it with?

madwilliamflint
10-19-2011, 04:26 PM
The abrasive blades are surprisingly durable so long as you keep the cut and the blade in the same plane and don't let it start bouncing around. Just give it some elbow and get 'er done.

For the dust on a one-off? Cut it outside. Put a fan at your back if there isn't much of a breeze.

Yeah I got a box fan I can set up behind me. Outside isn't much of an option as I'll be doing this until late tonight (tomorrow's drinkin' night and I have to do the finishing work on it on Friday for Saturday delivery.)

SGW
10-20-2011, 09:30 AM
I 'm with Lynnl. Are you sure you want to be associated with this? Even if the edge isn't "sharp" it could do a lot of damage if it was rigged to actually work, i.e. slide and drop. If I were taking this on I would make dang sure there was no way the blade could move in the final guillotine. All you need is a lawsuit because some drunken idiot mangled his finger.

madwilliamflint
10-20-2011, 04:34 PM
I 'm with Lynnl. Are you sure you want to be associated with this? Even if the edge isn't "sharp" it could do a lot of damage if it was rigged to actually work, i.e. slide and drop. If I were taking this on I would make dang sure there was no way the blade could move in the final guillotine. All you need is a lawsuit because some drunken idiot mangled his finger.

I did think about it and... I'm going with the fun over fearing litigation.

After all, if a frog had wings he wouldn't bump his arse when he hopped.

Oldbrock
10-20-2011, 05:21 PM
Angle grinder with a Zip Cut for the diagonal, do outside. Add a permanent stop so the blade can NEVER go all the way down. Peter

MotorradMike
10-20-2011, 05:52 PM
I have an idea.

Make the blade from Pine instead of 4130.
Easier to cut and looks WAY better in court.