Quick advice needed - enlarging a long blind hole

Hi,

There is no easy way to say this, so I'll be blunt - I made the most stupid mistake of my life. I built a boat with a PVC pipe for mast step/partner, which has an internal diameter of 80.5mm, and a carbon mast that is 81mm. All because I trusted the specs of the pipe, and didn't actually measure it (it should have been 82mm ID). Obviously, the mast doesn't fit.

The carbon mast is thin walled, so I can't thin it down without severely compromising it's strength. That means I need to somehow enlarge the hole of that PVC pipe. Here are a few pics from the build so you get an idea of what that pipe is.





The hole is 40cm deep. I have exactly 1 week to fix this, because that's the launch date for this boat.

Does anyone have any advice on how to make that ID of the pipe from 80.5mm to 82mm? The pipe has 5mm wall, so there's no worries about structural integrity, as long as the hole enlargement is concentric.

I had an idea to make a conical sanding drum (3D printed it since I don't have a lathe to make it from wood or something), wrap some sandpaper on it, stick a threaded rod in, put it in a drill, and send it down the hole.



First, the drum broke, then the drill stalled, and when I got a bigger drill, the rod twisted. Clearly this is not the way.

Can anyone suggest anything? Like I said, I am very limited in time. And yes, I feel incredibly stupid for making such an idiotic mistake... But I got to fix it no matter what.

 

I think working the existing tube in place will be hard. My kid bent some PVC tube using a heat gun.
I would either take a fresh piece of PVC and fix the ID/bore off the boat ad replace or wrap the mast end in cardboard covered in plastic film to increase its OD by 2-3mm and mold a new tube from fiberglass and resin. Another option would be to make some plywood plates with the correct ID hole and fiberglass them to the boat.

 

You would have to make an adjustable boring bar to do it.

If you still have access to the pipe, cut it between the supports, and enlarge the two remaining holes in the mast partner. Then epoxy a new larger pipe in between. To enlarge the holes there are several options available, holesaw, forsner bit, router, Dremel, etc.

 

Thanks for the suggestion, but the deck is enclosed now, the pipe is inaccessible, and there is no way to replace it, short of cutting half the boat open... I need to somehow modify the existing pipe, without taking it out.

 

Can't access it unfortunately... How would you suggest I make that boring bar?

 

Hi laukejas, you can get sanding 'discs' like what you made but made in the same way as a flappy disc, with sections of coarse or fine sandpaper glued into the core, with a 1/4 inch or 6mm pin to drive it. They come in various diameters, and a ~50 - 60mm diam would do your job, in 60 or 80 grit, 40 if you can get it. You will need a sturdy drive extension to fit it into, and into your drill. Get a couple, they can disintegrate after a while. Could pay to do the job upside down so PVC doesn't build up in the lower section, and have compressed air to blow it out, in case static charges keep the dust stuck to the inside. Keep the tube cool or it will melt and gum up inside. I hope you have a metal plate in the tube bottom so the mast doesn't eventually bore a neat round hole in the wood bottom from small rotations. good luck with your project. Don't believe sales people or shop's stated dimensions of anything, always measure for yourself.

 

Had to do this to a deep aluminum davit, got a cylinder hone and used a combo of heavy grit sand paper coil wrapped around the arms. Was long work as it was near 20 inches deep and we had to use a chuck extension. Eventually got it cut back, and hit it with a bubble hone for a polish. Not entirely sure if it would work on pvc.... but its worth a shot.

 

Another idea, buy, (expensive), or go to a metal engineering workshop and see if you can borrow an adjustable reamer for that size. It will cut mostly concentric when carefully turned by hand with an extension rod and T handle. Take the diameter out in stages or the tube will break. Blast the shavings out with air. The very bottom will likely need to be done with sandpaper flappy wheels as I mentioned above, due to the adjustable end section of the reamer not cutting. It may be quicker.

 

A hone would quickly get clogged. A boring bar can be made with a pipe of slighty smaller diameter and two or three cutting tools. The tools can be from a lathe, or small sharpened steel bars. They have to be adjustable, so as the hole gets bigger they can be shifted outwards. The metal bar gets turned with a drill or by hand. Alternatively, a 3 1/4 holesaw can be used to enlarge the hole.

 

We were just using the hone to hold shape of the paper it used against. Im guessing a hone with some heavy grit Emory cloth could help cut slow into pvc. Ive used the hole saw on other hole expander situations but never that deep, invariably it starts to wander in a softer material.

 

I actually like your idea best. But you have to make it robust and it has to be done slowly and probably with a makeshift press.

 

Piece of thick walled pipe, 25-50mm, steel, drill a hole trough it near the end. Take a bolt and four nuts, put the bolt trough the hole, two nuts on each side. Grind the end of the bolt to a sharp point. Adjust gradually to final size using the nuts (don't try to cut to much in one pass, it won't work). To turn it with a drill you need to weld on something that fits your drilk chuck (13mm bolt for example). Drill needs to have adjustable speed, 300rpm max. For hand turning drill another hole trough the end and stick something for a handle trough. You need to fabricate guides to keep it straight, so on the cutting end, below the cutter you stick a 80mm outside diameter bearing (for example 16010 with some tape around it to bring it to 80.5mm if necessary), and above it a 82mm one (for example 510019) floating. You cut the first 50mm or so using the lower guide only, then you jam the upper guide in the pipe. Or you could use some solid 3d printed bushings for guides.
It's the low cost homemade version of this: Milling Machine Boring Device 16 Handles Drilling Machine Boring Tool Holder 20 Boring Bar Blade 25 Adjustable Boring Tool Bar - AliExpress 202216001 https://de.aliexpress.com/i/1005005959839860.html?gatewayAdapt=glo2deu

Alternatively your hardware store should have 82mm holesaws for sale. They are used for installing electrical outlets in walls and come in two models, one with abrasive around the edge and one with cutter teeth welded in.
Like this: MADE in EU | Diamant Dosensenker 82mm - Bohrkrone 82mm günstig kaufen https://bergmann-professional.de/products/diamant-dosensenker-82mm-made-in-eu-diamantbohrkrone-82mm?srsltid=AfmBOoq5ufWk148OtZeJ4cL1350lLhmKboRJCd0i__A7HhyI7QlC9OWF
Or like this: https://bohrer-handel.de/products/m...yLAMxehwTr6BNgZN8C09u-cq8eER673Pc6Vl7kPZstc-4
For PVC even the cheapest one should work, but I recommend doing a test first.
These can be screwed onto a threaded bar to use as an extension.

 

Your conical gadget had little chance as there would have been contact all round the periphery and thus too much friction.A simple boring bar is just some kind of sharpened piece of steel in a bar that fits a drill chuck and a guidance system for the bar.In this case I would recommend making some plywood discs-at least 15mm thick and at least two at 80.4mm diameter and at least 2 at 82mm diameter.I am attempting to upload an image of what the business end should look like and it ought to have one of the 80.4mm discs at the lower end.Do your best job of keeping it vertical until one of the 82mm discs can be added to the part of the central bar and slid into the enlarged hole.Once you have both discs guiding your direction,it should be fairly straightforward.

You may find it helpful to add an overlapping flange to the upper plywood disc to prevent it dropping.The diameter can be adjusted to achieve a good fit and you may need to make extra guide discs if the bar flexes or the first cut isn't exactly the required size.The top of the boring bar may need to have a smaller spigot to suit your drill chuck.Obviously,you will need to determine when the hole has reached maximum depth.

 

Thank you for responding so quickly and offering so many suggestions, guys. I think any of them would work, but I'll address some of the concerns due to the limitations I have. Mainly that I don't have any welding equipment (and no time to find any to borrow), so even attaching a T-nut at the end of the bar so that it can rotate the drum that I made was had to be done with epoxy. That limits some of what I can do. No welder, no lathe, basically I just have a hacksaw and an angle grinder.

The bottom of the hole of this mast is epoxy and 3 layers of fiberglass, 5mm thickness in total. I figured it should be enough. The issue with most of the methods you guys suggested is that the very end of the hole would not get cut, as the cutter would sit at least a few mm above the end of the boring/sanding rod. My conical sander had the same issue. Or, the guide bearings would get in the way. I suppose maybe it should be possible to modify the tool just before the end (remove the lower guides) and hope for the best.

I had this idea, but if the sander is smaller than the pipe, I would have to keep rotating it around to try and increase the diameter evenly, without knowing how much I'm taking off, and if I'm not wandering off or making an elipse. And working blind in a 40cm hole, with massive sideways torque required to press that drum against the side of the wall sufficiently for sandpaper to work... I don't see how I could succeed with this, at least with my skills :/

Good idea, but I can't find any for sale of that size. I'll call around a few shops on Monday.

This seems to be the easiest solution so far... I just don't know how to keep this thing centered, as it will definitely want to wander off. Maybe I could keep it centered by gluing on a guide disk on the bottom guide drill, and a few more on top, on the hex bit part. But the sheet metal of this cutter would also want to bend inwards because the pipe is already very close to that required diameter. Also I don't know how it would deal with the end of the hole, I would have to take off the lower guide, cut off the guide drill, and somehow know when to stop - visibility is pretty much zero inside that hole, even without any debris. Also, I'd somehow need to extend the hex end to reach deep into the hole... Maybe there are such extensions, I'll search around.

Rumars, you also suggested this, it does seem like a good idea, but I'm not sure how to deal with centering this thing, and making sure it can work the end of the hole without cutting into the bottom epoxy plate (like I said, visibility is zero down there).

I just realized... The pipe is not an ideal circle, it is somewhat eliptical. 80.5mm ID that I mentioned actually varies from 80.1 to 80.9 or so. So any guides that I make would have to be somewhat undersized and would likely introduce a wander... Or maybe not, I'm not sure.


I just got another idea. What if I make a drum to hold a sandpaper flail, something like this:



This should have far less friction than the drum I made. The strips of sandpaper would extend from the centripital force and wear down the pipe walls. I could 3D print a 82mm disk that I would place just above the flail, and it would only allow passing the tool further into the hole when the flail already expanded it enough. Could this work?


EDIT: I found a 82mm cutter in my local hardware store: Deimantinė gręžimo karūna SPECIALIST+, 82 mm https://www.ermitazas.lt/p/deimantine-grezimo-karuna-specialist-82-mm-tvcye9g3 (sorry it's in Lithuanian, but there are pictures). Would this work? I just realized it should probably be self-centering after the first few cm, but what about the start of the hole, how do I center it at the beginning? As for the end, I figure I could glue on a small piece of scrap to the center drill thingy (the drill would be cut off), so it would bottom out against the epoxy bottom of the PVC pipe and would allow this thing to pass no further. What do you guys think?

 

Glad to see that you have read and considered the suggestions.I did recommend making at least two guide discs at 82mm-which means that near the bottom of the hole,they would both be above the cutting portion of the boring bar I rapidly modelled.As for cutting the entire length,just slant the cutter downwards at it's outer end.If you don't have welding or other useful facilities you may have to wave money in front of somebody who does or offer them something your expertise can do and which they might need done,either now or in the future.I am quite confident that your flap wheel won't be accurate or rapid,but it will probably rotate without too much complaint.

The 82mm holesaw would do the job but would need the same arrangements of guide discs that I advised and you would need to find an extended arbor to reach the full depth of the hole.You would also need a rather powerful drill to turn it.