How to cut a 96mm hole in my van's roof?

GervisLooper

I want to make a hole for the flessner 2000 airvent which requires a 96mm hole. Hole saws that I have seen do not sell in that exact size. The closest I have seen is 86mm. Would it be hard to file another 10mm to make it to 96 or nay bother?

Best way or any other suggestions?

Apparently a jigsaw can be used however I don't have one and even if I did it seems it would be very delicate work to make a perfect circle vs the hole saw way.

Grenage

95mm: https://www.ebay.co.uk/itm/402024552141

I have no doubt you can get a 96mm, but it might not be at a price you like.  You could stitch-drill the circle and then join it up with a jigsaw.  I assume the flange will cover the edge, in which case it wouldn't need to look perfect.

Eldi_Dos

I would think a hydraulic knockout punch cutter would do the neatest job.
Try caravan storage yards who might point you in the right direction or a small fabrication workshop.

ThisIsWeird

Confirm with Flessner, but I suspect a 100mm hole will be perfectly ok - and a cutter that size should be cheaper.

Or, I'm pretty sure one of these will do - consider it a disposable item if needed: https://www.ebay.co.uk/itm/363880772448? I bet it'll survive and can be reused on other materials afterwards. This will almost certainly do a decent job through a steel body panel.

I'd drill from the inside first to make the central drill hole, and then do a gentle part-cut from outside - just enough for a nice groove - and then go back to the inside to finish it off - there should be less burr. Nice and slow and steady. Put masking tape over the outside to protect the paintwork from hot swarf.

FFHillbilly

cutting thin sheet metal with a ~96mm holesaw is not going to be precise at all, and by the time you have all the burrs filled off I think you'd probably end up with some sort of oval about 100mm on the longest side if it went well.
so I would go smaller, the 95mm would be ok I think. find out the maximum the hole can be before the vent either falls through or fixing it in place becomes difficult

FreeBear

FFHillbilly said:

cutting thin sheet metal with a ~96mm holesaw is not going to be precise at all, and by the time you have all the burrs filled off I think you'd probably end up with some sort of oval about 100mm on the longest side if it went well.

When I've needed to cut a hole in a thin sheet of metal, putting a block of wood behind has always helped. For small holes, I have a selection of Q-Max hole punches, but the largest one available is 80mm i think (and also darned expensive). I would recommend using a nibbler to remove the bulk of the material, and then a combination of a die grinder and half round file to finish it off. For a one-off job grab one of these - https://www.ebay.co.uk/itm/385309154223

ThisIsWeird

FreeBear said:
I would recommend using a nibbler to remove the bulk of the material, and then a combination of a die grinder and half round file to finish it off. For a one-off job grab one of these - https://www.ebay.co.uk/itm/385309154223

Blimey! Never seen one of these before. Easy to control and guide? Worth making an MDF template to contain it? Still sounds like a lot of work with the finishing off.
I still think my suggestion will work, should be accurate enough straight-off, and should require little finishing or deburring. 

Section62

ThisIsWeird said:

FreeBear said:
I would recommend using a nibbler to remove the bulk of the material, and then a combination of a die grinder and half round file to finish it off. For a one-off job grab one of these - https://www.ebay.co.uk/itm/385309154223

 ...Easy to control and guide? Worth making an MDF template to contain it?

Yes-ish, and yes.  Nibblers are great for this kind of work, but the vibration can make them tricky for fine work, so using a template is a good idea.  For cutting a circle you have to make the template 'x'mm larger than the finished hole, with the 'x' depending on the measurements of the cutter head (can be tricky to work out first time).

I've not used one of the drill attachments so can't comment on how robust they are (as FreeBear says, a one-off job should be ok with care) but the electric and compressed-air ones make easy work of cutting sheet.

Things to be aware of is the need for clearance between the cut edge and other stuff (e.g. a stiffening rib on the van roof) and also that the 'output' from the cutter is typically sharp crescent-shaped pieces of metal which have a habit of cutting anything which they come into contact with.

The finished edge should be burr-free and fairly smooth (if you use a template or straightedge) though.

daveyjp

Drive van to a metal fabricator, get them to cut the hole, give them a few quid beer money,

ThisIsWeird

daveyjp said:

Drive van to a metal fabricator, get them to cut the hole, give them a few quid beer money,

Hmmm.

A bit risky, I think. Setting it all up for the job is likely more involved than you think, and there's also things like access to the roof, protecting the paintwork, that sort of stuff - which they might not be too bothered about if they think you are after a "Got 10 minutes?" job.

On the other hand, if it's marked out and can be done fully from inside, then it's another possibility. I'd hope they'd be aware of things like risk from heat to the paintwork.

FreeBear

daveyjp said:

Drive van to a metal fabricator, get them to cut the hole, give them a few quid beer money,

If they use a plasma cutter, it will be very quick. Just need to watch the splatter doesn't set fire to anything. A flap wheel will clean the dross off, and you should end up with a fairly neat hole. But there will be some heat damage that will require treating with a rust inhibitor, primer, and then top coat.