Cutting stainless steel

What I thought would be a simple re and re looks to be difficult.
I am replacing my thru hull exhaust for my Webasto AT 5000st furnance.
The present above waterline thru hull is 90 degrees and blows on a rub rail causing discolouration. The exhaust thru hull I want to install blows straight out. However the diameter of the present thru hull is 1” and the diameter of the new thru hull is 1 1/2”. The thru hull is mounted to a 1/4” stainless steel plate that is epoxied or glued to the hull.

What type of drill bit or cutting method would be best to enlarge this hole through a 1/4” stainless steel plate?

Tapered reamer or step drill is what I would use. It will leave a clean hole with minimal fight.

I knew I could count on trawler forum.
Considering the cost of such a bit , 1 1/2”, what’s better ; carbide tip, titanium or cobalt?

And while I’m on the topic has any one used a carbide tipped masonry drill for stainless

Best way would be a CNC milling machine. A little expensive for just the one job though.

You can get through it with a hole saw, carbide tipped one might be a little better, but a HSS one will do it with care. You will need to clamp it firmly in a drill press to get sufficient pressure. A carbide bit in a die grinder would also do it freehand, given some patience. A step drill that big is expensive and may not make it all the way through, it has only one cutting edge.

If you can't remove it from the hull I'd use the die grinder. You can buy a 1 1/2" twist drill bit but it can't reasonably be used in a hand drill.

Greetings,
Mr. g. When working stainless, do so slowly with LOTS of coolant/lubricant. Once you harden (heat it up) the stainless, you're sunk.

I think the first thing I would do is to try to remove the plate from the hull. If you can get it off it will open up the possibility of taking it to a machine shop to enlarge the hole. Some heat may make it possible to get it off by softening the epoxy or glue. If you can’t get it off then maybe a jigsaw and a lot of cutting oil. Slow speed with little forward pressure on the saw to keep the blade cooler. As said above if you let it get hot you are in deep dodo.

To answer your question about using a masonry bit: I would not expect any success.
A Cobalt alloy drill bit is a good choice for stainless. Black oxide can also be used.

McMaster-Carr has a 1"-1.625" step drill for about $103. It will fit a 1/2" drill motor.
That would be my first choice if you can work around the extra 1/8" diameter.

A 1.5" twist drill would be my second choice and will leave a 1.5" hole which is good.
A heavy duty drill motor such as the Milwaukee Hole Hawg will handle these nicely.

McMaster-Carr has the appropriate lubricant, too, if you don't. Use a nice slow speed.

If possible to remove the stainless plate (try heat as Comodave suggests) it would be worth the trouble. Then you have the option to replace it with the right size. If its a custom piece, then you can at least do the work in the shop and not in an awkward spot on the boat. Better yet you can take it to a machine shop and have it done perfectly for very little money. You may spend more for cutting tools than it would cost you to have it done by a pro with a full shop.

Comodave said:

I think the first thing I would do is to try to remove the plate from the hull. If you can get it off it will open up the possibility of taking it to a machine shop to enlarge the hole.

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Or throw it away. The new fitting doesn't require a metal plate, right?

grahamdouglass said:

What I thought would be a simple re and re looks to be difficult.
I am replacing my thru hull exhaust for my Webasto AT 5000st furnance.
The present above waterline thru hull is 90 degrees and blows on a rub rail causing discolouration. The exhaust thru hull I want to install blows straight out. However the diameter of the present thru hull is 1” and the diameter of the new thru hull is 1 1/2”. The thru hull is mounted to a 1/4” stainless steel plate that is epoxied or glued to the hull.

What type of drill bit or cutting method would be best to enlarge this hole through a 1/4” stainless steel plate?

Click to expand...

I presently have a thru hull exhaust from the old Espar D7L that I removed several years ago. My boat is at RVYC Coal Harbour. If we can get together, you can have the old exhaust, as it is straight and should fit your needs. If you haven't yet modified your new one, you should be able to return it. Send me a PM

guy with a boat said:

If possible to remove the stainless plate (try heat as Comodave suggests) it would be worth the trouble. Then you have the option to replace it with the right size. If its a custom piece, then you can at least do the work in the shop and not in an awkward spot on the boat. Better yet you can take it to a machine shop and have it done perfectly for very little money. You may spend more for cutting tools than it would cost you to have it done by a pro with a full shop.

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This is the way.

"I'd use the die grinder".

And use a tiny hand router folks usually use to fit electric boxes behind wall board.

They are really cheap , and just be sure it accepts 1/4 inch shaft on the die grinder.

Wear eye protection !!!

RT Firefly said:

Greetings,
Mr. g. When working stainless, do so slowly with LOTS of coolant/lubricant. Once you harden (heat it up) the stainless, you're sunk.

Click to expand...

I was a tool & die maker in a previous life & RT's comment is right on the money!

i use a hole saw for cutting stainless all the time. fine tooth is better if you can find them. i use the ones from this company: http://www.mo2ls.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=mpt&Category_Code=ROSCF
no affiliation.
when i need to upsize the hole, use an adapter like this:https://www.rockler.com/copilot-hol...x72DTHmYsSuLqCktf_B_ejMKGjtwxzRQaAt9-EALw_wcB

the whole key to working stainless is cutter speed and pressure. i use either rapid tap or tap-matic for cutting fluid, but there's a lot of things you can use for coolant/lube.
you need to remove enough metal when cutting to help keep the surface from overheating. low speed, fairly high pressure, decent lube. hold the workpiece securely so it doesn't move around.
using a drill press or other similar machine is preferable to doing it by hand.

RT Firefly said:

Greetings,
Mr. g. When working stainless, do so slowly with LOTS of coolant/lubricant. Once you harden (heat it up) the stainless, you're sunk.

Click to expand...

Not to get all pedantic on you, but it isn't heat that hardens stainless steel. 316 stainless does not heat harden. It is rubbing it without cutting. You need to cut a minimum of about 0.001 per tooth or you will work harden the surface, going from not much harder than aluminum to about the hardness of tool steel. That requires more pressure on even a modest size bit than you can apply with a hand drill.

I would MUCH rather attack that in situ with a die grinder that a 1.5" twist drill in a hand held motor. The hole will be ugly and you might end up with a broken wrist when it catches. A step drill will be much better controlled if you must go that way. Die grinder will take time, but you will not hurt yourself and have a nice hole at the end. Get one from Harbor Freight for $20, it will last at least the one hole.

If you want to use a taper reamer get one for metal. It will most likely one and done for the tool. I would go slow and keep oil on it for cooling. Good luck.

grahamdouglass said:

What I thought would be a simple re and re looks to be difficult.
I am replacing my thru hull exhaust for my Webasto AT 5000st furnance.
The present above waterline thru hull is 90 degrees and blows on a rub rail causing discolouration. The exhaust thru hull I want to install blows straight out. However the diameter of the present thru hull is 1” and the diameter of the new thru hull is 1 1/2”. The thru hull is mounted to a 1/4” stainless steel plate that is epoxied or glued to the hull.

Click to expand...

I am not familiar with your exhaust pipe, but could you not simply add another 90° elbow and give the exhaust a new direction? And get it a little bit further away from your rub rail?

I'm surprised nobody has questioned the type of SS. In my experience some can be a lot easier to cut than others.

I remember one time trying to drill through a bolster end on a pocket knife. Regular HSS twist drill bits wouldn't even scratch it. I got a cobalt bit and it went through it almost like butter...well not really, but pretty easy.
Other times with different projects, and different bits...I've tried cobalt drills that didn't cut hard materials well at all. a lot of variability with the bits too....

1/4" SS plate?? sideways drilling, grinding and chopping will get very old. Do almost anything to get it off the boat, and off to a milling machine.

A little up date

The weather turned cold and miserable so this job will probably be done when it is a lot warmer, mabey May mabey never. I stopped selling my soul to the boat Gods a while back. The original exhaust will be put back on till then.
There is also a problem with a code 2 on my Webasto Airtop 5000st. This has to do with the flame sensor. The furnace is on my bench, at home, so I can do a service. I hope it is nothing more than a good cleaning. Webasto parts are insanely expensive. I was quoted a minimum $1000 to re & re the flame sensor and bench test it.

I also bought a 1 1/2" cobalt hole drill, so I hope that will do the trick when and if I get around to this project. Thanks for the input.

I think Jigsaw would be helpful, Bosch JS470E jigsaw can cut up to 3/8" steel

Take a cut off wheel and cut the existing elbow to any degree you want

slowjoe said:

Take a cut off wheel and cut the existing elbow to any degree you want

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And take it to the dock.