Cutting hole in 4mm steel cabin roof.

[Matt and Miriam]

Our composting toilet arrived today, but with it comes the need to cut a 3" diameter hole in the cabin roof for the vent, which is somewhat daunting.

Am I right in thinking the easiest way would be using a holesaw like this?

Anyone done any different, drilling holes and jigging the hole out?

[charles123]

Using one of these is the conventional way, it wont be easy, take your time, use a low speed on your drill, assuming its variable speed. If using it too fast it will wear it out quickly. Take it in stages to let everything cool off. Its unlikely but if the metal gets too hot with everything bone dry it could set fire to what is under the metal so be sure the bare metal is already exposed inside the hull where the hole will be

 

good luck

[david and julie]

You could do it with the holesaw (if you have a good quality drill) but it is not the cheapest way because you may never use the holesaw or its mandrill again.

 

Personally I would use a jigsaw with the correct blade, which is a lot easier than you think.

 

Eitherway, use cutting or lubricating oil on the blade/bit will make it last longer.

[blackrose]

You'll have a hard time with a hole cutter of that size unless the part of the roof you're cutting is fairly flat. The torque on a cutter of that size makes it quite hard to hold the drill firmly. I would mark up where you want to cut and drill a series of small holes around the circumference of the circle. The first hole should be big enough for you to get a jigsaw blade in (anout 6mm), the others can be smaller. Then use a jigsaw with a metal cutting blade to join up the holes. If you have a decent jigsaw it's not that difficult. Wear goggles and use a bit of cutting fluid or WD40 and go slowly.

 

You dont actually need to cut a perfect hole - presumably you are fitting some sort of collar on the ouside and you can weatherproof it all afterwards with some PU sealant such as marineflex.

Edited August 1, 2006 by blackrose

[Cafnod]

Hi

If you are going to use a hole saw buy a Starrett or an Irwin, they a little dear but the best on the market.

Drill a 6mm pilot hole in the centre, then use the drill on the slowest setting. I use an 850 watt Bosch for cutters of this diameter and greater. Do use plenty of lubricant, cutting paste, oil, WD40, whatever you have but do not get it in the cut, it is an offense that will get you a large fine. If necessary make a dam out of plastecene, or get a rag to catch excess lubricant. Make sure the drill has a side handle and keep hold of it. I regulalry use holesaws up to 125mm without problems, just take it slowly and carefully.

If doing it the old fashioned way get a compass and mark a circle of thye required diameter. Centre dot punch holes every 4mm. Drill the punched holes with a 3mm bit. I normally start the cutting out with an abrafile or a needlefile, then I either use a junior hacksaw blade or a jigsaw.

You can do the complete job with a jigsaw, either boring a large start hole slightly to the inside of the circle line.

Or if there is a nearby boatyard they will do it very fast with a plasma cutter for not a lot (depending on the boatyard).

[DHutch]

I'd do with the jigsaw, you need a suiitable metal blade for it, then draw the circle, drill one hole, and cut round in one go, nice a slow, keeping on the line. Shouldnt take long.

 

The holesaw would work, but even with a good one, and a powerfull slow speed drill that con provide the toque needed you'd have a job without it being in a piller-drill.

- Using a hole saw even on mild steel needs it taking slow, with lots of power, not going at it at 1800rpm and just blunting the saw and warming it all up! (stainless steel is even worse)

 

Otherwise if you dont have a jigsaw, you could do it by driling many holes and then linking them with round file or simular, then tidying up with a halfround file. But that would be slow.

 

 

Daniel

[Jus73]

I would recommend the Bosch powerchange holesaws you highlighted through screwfix. They are some much more easier to use the standard holesaws. I used a similar sized holesaw for the brass pumpout fitting on the gunnel and had no problem cutting through in a few minutes. Just take your time!

 

Just.

[Matt and Miriam]

Thankyou for all for all the pointers. Still not sure which way i'll go. Seems it should be nice and slow with plenty of lube either way

 

The only thing i've done on the steel so far is drilling through the hatch and runners so we could padlock the hatch and make the boat secure when we weren't on it. Don't think the drill I've got would be up for cutting through the cabin roof so i'd need to hire/invest in something better if i went down that route.

 

Swinging a little more towards jigging the hole out. If I decided to do that would I be best buying a decent electric jigsaw, which i'd have plenty of use for when it came to lining and fitting out, or just using a junior hacksaw?

Edited August 1, 2006 by Matt and Miriam

[david and julie]

If you are only just starting to fit out a shell you may well need both a jigsaw and a hole saw anyway.

 

Jigsaws are helpful for all manner of jobs plus you will need holesaws to fit skin fittings for sinks, bilge pumps, and to put wiring and pipework through bulkheads etc.

 

I don't think you meant a junior hacksaw.

 

I would buy the best jigsaw you can afford, within reason. A jigsaw with a new, good quality, blade will cut that hole in about 5 mins, it will not be hard to do Avoid the really cheap tools and bits, they are a false economy.

 

Is this a refit/new fit out?

[Matt and Miriam]

New fit out. We took delivery last thursday of one of Ledgard Bridges narrow beam barges. Pictures posted intermittently at www.nbexodus.blogspot.com.

[david and julie]

Very nice boat.

 

When I started ours I bought some secondhand but top quality powertools(De-walt /Hilti etc) off Ebay with the intention of putting them back on sale at the end of the job. If you are using hardwoods(like you should be on a nice boat like that ) you need tools which are man enough for the job.

 

Best wishes with your fit out.

[DHutch]

Yeah, not sure about the holesaw, but a jigsaw and a decent drill are an great investment, and unless you get cheap tat should last a life time. And power tools (even good ones) are rediculasly cheap.

- Our jigsaw is a bosch that my grandad bought about 20years ago, and its as good as new. (we borrowed it for so long he got a new one)

- And the powerdrill on the boat my other grandad bought for the inhouse joiner of the builder mercharchance he ran about 50years ago. Its been hammered for years and after two set of new brushes, its still a cracking unit!

 

 

Daniel

[Cafnod]

On power tools I have a Bosch drill that is about 17 years old, biggest model they did at the time, it handles holecutters up to 125mm, although I have only used 102mm in steel. It is still on its first set of brushes but I am looking for its thrid chuck, too many big holesaws.

Jigsaw is an industrial AEG used it in steel up to 6mm.

Rest of the stuff is mainly Hitachi (235mm circular saw, cordless drills, recip saw, M12 router, cordless circ saw) it is low end industrial and is very good indeed.

If you are very serious about you fitout a table saw and router table will work wonders, both in dimensioning and finishing timber. I have found a Trton workcentre excellent as a portable solution that enable the use of power tools. Once set up amazingly accurate.

[blackrose]

I'd do with the jigsaw, you need a suiitable metal blade for it, then draw the circle, drill one hole, and cut round in one go, nice a slow, keeping on the line. Shouldnt take long.

 

You'll have a hard time turning the jigsaw blade around a 1.5" radius that's why I suggested a series of holes that you link up with the saw.

 

I changed my mind about the hole cutter, I imagined it was a bigger hole. 3" dia isn't that big so it would work ok and probably give you a better result, but take the others advice on using a decent drill with side handle & good cutter.

 

Basically, bigger holes are easier with a jigsaw as you have more ability to turn the blade through a larger radius, and smaller holes are easier with a hole cutter because the torque isn't such a problem.

 

You can always start with a drill & hole cutter and if that doesn't work go to plan B and use a jigsaw. You'll always use the gear for other jobs apart from the hole cutter perhaps.

[elessina]

Am I right in thinking the easiest way would be using a holesaw like this?

Anyone done any different, drilling holes and jigging the hole out?

Matt,

 

I have cut many holes on our barge, including 3" with similar holesaw set from screwfix (£35 for set of 11) see screfix holesaw. As previously stated, select slow speed and use a lot of cutting fluid, Vaseline or even water. My 76mm cutter started to wear (blunt!) on the 4th hole I cut, so I used the 71mm cutter. The smaller cutters have seen maybe 20 holes in steel, some have a tooth missing, others well used, but all still usable. Actually when cutting through the roof, I found Vaseline very good as it helped stop all the metal filings / swarf from blowing around on the paintwork, which when trod on get impregnated in the paint and rust.

 

For a 3" hole, best drill to use is one with a mechanical 2 speed gearbox. I did try with a cheap (£15) drill but burnt it out after about 6 holes.

 

You may also find this page useful for some DIY tools diy tools

 

Ian

DB Elessina.

[Matt and Miriam]

Matt,

 

I have cut many holes on our barge, including 3" with similar holesaw set from screwfix (£35 for set of 11) see screfix holesaw. As previously stated, select slow speed and use a lot of cutting fluid, Vaseline or even water. My 76mm cutter started to wear (blunt!) on the 4th hole I cut, so I used the 71mm cutter. The smaller cutters have seen maybe 20 holes in steel, some have a tooth missing, others well used, but all still usable. Actually when cutting through the roof, I found Vaseline very good as it helped stop all the metal filings / swarf from blowing around on the paintwork, which when trod on get impregnated in the paint and rust.

 

For a 3" hole, best drill to use is one with a mechanical 2 speed gearbox. I did try with a cheap (£15) drill but burnt it out after about 6 holes.

 

You may also find this page useful for some DIY tools diy tools

 

Ian

DB Elessina.

 

Ian,

Have the holes you've cut with the holesaws been in flat steel or curved? I'm getting tempted to invest in a decent drill and go with a holesaw as I imagine the finished hole being much neater but don't know how well it would with the curve of the roof? I don't want the flue to come out at a daft angle!

Cheers,

Matt.

[Richard Bustens]

I used the bosch ones up to 100 mm in 10mm steel the only problem is i burnt out 2 drills trying to drill so slow so i bought a cheep STA impact drill that i could switch off the impactor fron b&q this is a very slow drill and i have had no problems with it.

[elessina]

Ian,

Have the holes you've cut with the holesaws been in flat steel or curved? I'm getting tempted to invest in a decent drill and go with a holesaw as I imagine the finished hole being much neater but don't know how well it would with the curve of the roof? I don't want the flue to come out at a daft angle!

Cheers,

Matt.

 

Matt, they were on the curved roof, I believe the steel was 4mm thick. The 3" holes I cut in the roof were for ventilation (mushroom type vents). I found the holes cut were a few mm larger than the holesaw, so the 71mm holesaw gave a good round hole around 74mm diameter. Be carfull where you cut, there may be cross braces, often at 2 feet intervals. If you have downlighters in the roof inside, remove these and through the 2" hole you will be able to see / find the cross brace locations. I also used a magnet to help collect the swarf.

Ian

[Hairy-Neil]

I've cut 3" holes in the side of 4" pipe with a hole saw. Can't get much more curvature than that. It was done clamped down in a pillar drill though.

[Cafnod]

You should be fine even on a curved roof, the holesaw will start on the raised part first, but dont worry, keep the drill upright. My Bosch has a mechanical gearbox, think it is a CSB 2 850 RET probably long since obsolete. But I have drilled all the pump out vents skin fittings and done all of the chain drilling for electrical socket and chimeny with it, plus loads of 20mm holesaw cuts for conduit and cable glands and pipes through the front and rear bulkheads, and BTW none of my starrett hole cutters have been blunted or lost teeth after a few holes, that is why they are the choice of boat builders, steel fabricators and electricians all over Europe and north America.

[Matt and Miriam]

Thanks, it's nice to know people have done what I'm planning to do and it works. Am away for a week but will be investing in decent tools before I do the job. Will let you know how it went...

[nmptwentyone]

think id probably go for the hole saw too, seeing as its a one off. i use them all the time on 2mm. im sure if you take it easy it'll do 4mm with no trouble.

 

Could you let me know how you get on with the toilet itself. just had a look at the website. considering it for my sailaway i hope to take delivery of early next year.

 

thanks

[Richard Bustens]

I used the Bosch ones on 10mm and cut about 12 holes , just bought a Dewalt one coz the company i use had stoped selling the Bosch ones, Had to get a new spigot for it but it seems better than the Bosch.

[John Orentas]

I used the Bosch ones on 10mm and cut about 12 holes , just bought a Dewalt one coz the company i use had stoped selling the Bosch ones, Had to get a new spigot for it but it seems better than the Bosch.

 

 

I agree with pretty much all that has been said, a good jigsaw with the correct blades or a quality hole-saw in a very slow drill will cope with 4mm steel without problems. Remember though to use a coolant /lubricant of some kind, any kind of oil will do or even soapy water is better than nothing, makes your blades last much longer.

 

For cutting several or larger apertures think about a Plasma cutter, when I was in business I would regularly hire one for a couple of days at a time, just a few years ago the rate was £40 per day. I think that in most towns there will be a company who offer the service. These things are incredible after two minutes instruction you can be cutting through steel plate at walking pace, no burning, no distortion the tool simply removes a 1mm wide strip leaving the edges with hardly any discolouration and little need for finishing.

Edited August 8, 2006 by John Orentas

[DHutch]

For cutting several or larger apertures think about a Plasma cutter, when I was in business I would regularly hire one for a couple of days at a time, just a few years ago the rate was £40 per day. I think that in most towns there will be a company who offer the service. These things are incredible after two minutes instruction you can be cutting through steel plate at walking pace, no burning, no distortion the tool simply removes a 1mm wide strip leaving the edges with hardly any discolouration and little need for finishing.

Thats an interesting idea actally.

- I used a plasma cutter a few times, and you right, its a truly amasing beast!

- Hadnt though about the possabilty of hiring one tho! But at £50/60 a day, thats quite reasonable.

- Even if not sutable for this job, its certainly worth considering if your cutting out windows isnt it.

 

 

Daniel