How to best make 4 1/2" hole

[rickeieio]

As the title says, I need to put 6- 4 1/2" holes in 3/16" plate for tail and reverse lights on my bed.  Last time I did this, I used a plasma cutter with barely acceptable results.  My options seem to be: plasma, reciprocal, or hole saw.  If I use the hole saw, I think using a correct sized hole in a plate as a guide would help keep the hole true to size.

Any other suggestions?  I'm not good enough with a torch to go that route..........And Georgia Hybrid, I'm not good enough with a .45 either.

[GlennWest]

Holesaw uses a pilot bit so should stay true. I would use a torch but I am a professional with one. Also have a circle burner for a torch

[GlennWest]

Cheap circle burner. Weld a washer to a rod sized to fit torch tip. Weld a short rod sharpened on end to a 1/4' pipe nipple. Drill and tap a 1/4" hole for a set screw. Slide it on rod. Place on torch. Adjust to hole needed. 

[rickeieio]

I have a circle guide for the plasma.  Holes were still a bit rough.  I would think a torch, in my hands, would just as bad or worse.  Hole saw does have a center bit, which gradually makes the center hole a little bigger as it wallers (farmer speak) around.  Result, hole not round.

I have the old mounting plate for the factory lights, which I'll re-use.  I might clamp that plate to the sheet steel as a guide.

[GlennWest]

A plasma should be a fairly clean hole. Nothing a file shouldn't clean up. Tip good?

[spindrift]

Call Ranch Hand, or similar manufacturer.  Ask them how they do it.

[GlennWest]

They likely punch them out. They make tool for that. Too costly for one time use

[Darryl&Rita]

Did ours with a laser. Also expensive. Use a plasma or torch, slightly undersize, then grind to the line with a pencil grinder.

[Moresmoke]

If the plate is still loose or better yet you don’t have it yet, find a shop with a laser table. When I hire parts cut, it typically doesn’t cost much more than the steel costs me.

If it is already part of the bed, take your hole saw and cut a hole through a piece of 3/4 plywood. Clamp the plywood to the plate and you will have a guide to hold the saw in the right spot.

[rickeieio]

I'm going to get a hole saw and try it on a piece of scrap.  If that doesn't suit me, I'll break out the plasma.

[Darryl&Rita]

Don't forget, there's a pretty good lip on the rubber mounting ring for the lights that will help hide all but the worst of errors.

[mr. cob]

Howdy Rick,

Using the plywood as a guide is a darn good idea, however using a hole saw to cut that size hole in 3/16" steel is going to take a good heavy duty drill to drive it and a high quality hole saw that will probably be dull when the job is done, that's a lot of metal to be removed and a cheap hole saw ain't gonna do it.  If you try it with a cheap hole saw it will get dull and work harden the steel, this will knock the edge off of the good hole saw you will buy to finish the job, cheaper to spend the money on a good hole saw to begin with, take my word on this, been there, done that.

Dave

[Steve from SoCal]

If you do use a plasma torch make a template and keep the torch at the same angle.     Plasma at least hand held plasma torches are real sensitive to angle on thicker material.     They also don't pierce cleanly, start your cut inside the circle and ramp into the radius.    The mention of good tip is another big thing with plasma, a worn tip and consumables will be frustrating at best.  

A hole saw at that diameter could be a wrist breaker in a hand held drill, use a slow speed.    At that size I would rather use a jigsaw.

[rickeieio]

Went to the hardware store this morning, and they only had cheap hole saws.  This store used to carry good stuff, but they're now sitting between a Home Depot and a Lowes.  Quality suffers.  So, at $36 for a cheap saw, it's $6/hole, if the thing lasts that long.  Plasma to rough it out and a hand grinder to finish.  I can use the original light mounts for the template, making for less grinding.

I used to buy my metal cutting blades from this same store.  They handled the 8" Milwaukee blades.  No more.  Now the best they have is 7 1/4" Irwin.  They don't last very long.......

[GlennWest]

I have found this true on the last few jobs I have been on. 

[rpsinc]

I certainly have seen the overall quality of abrasives decline over the last 10 years.  We are all pretty much responsible for it.  We want the best quality for the cheapest price and those lines rarely cross.  And with the advent of CNC machines, either tables or mills, the work you are doing is done less and less, so less demand for those types of abrasives(hole saw).  Finding good quality grinding and cutting wheels is more difficult.  I have used Metabo Slicers and Slicer Plus for many years.  They dont seem to work as long as I remember.  But perhaps that is a ME issue, not a they issue.  In any case, the cost for consumables continues to increase for all my projects.