Portholes

February 1, 2021

As mentioned a few weeks back I’ve been making a circle cutting jig to allow me to cut holes in the front door to fit some portholes. The weather has been a bit frosty so we’ve been waiting for a warmer day. Also some more materials needed to be ordered to allow the job to be done.

When we measured up the door for fitting we hadn’t allowed for the rebate that was needed on the front side. So I needed an extra bit of packing on the rear. I ordered up some plywood that was pre-cut into disks to save a bit of time. To find the centre I used a geometry trick with a square which finds to points on the circle that are exactly opposite each other. The can be joined and the process repeated to find the centre. I then adjusted the jig for the size needed and cut the slot. I left tabs as recommended. Once the centre was cut I then marked up for the bolt holes using the porthole as a templated and drilled them to fit the joint connector nuts on the inside porthole face. I then varnished the disks using a coloured varnish to match the door.

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Next up was marking out the doors. We did this in place by putting the porthole at eye height and putting some tape below the hole. We then measured up from that line and marked the centre. For the left/right position we marked the centre of the inner frame.

Once the door was removed and placed over 2 workbenches the next step was to drill the centre holes, a long 6mm auger bit was used. As the door has a ridged surface a rebate was needed so the portholes would fit flush and have no gaps for the rain to get in.

A large cutter was fitted in the router and the position adjusted so that the outside of the cutter was half the diameter of the porthole. If doing this step again in future I would add a bit more tolerance here maybe an extra mm as the rebate did need some fine-tuning with a chisel to fit the porthole. The depth stop was also adjusted so that the cutter would just cut into the main part of the door.

Once the rebate was cut, a smaller cutter was fitted and the jig adjusted for the through hole. As with the packing pieces the slot was cut with some tabs in it so that the disk would not move whilst cutting. It was during this step I realised that the door was hollow with some strengthening pieces. Also that the maximum depth of the router was not going to be sufficient to get through those solid sections.

After repeating the process on the other side I cut through the remaining tabs, prized off the plywood skin and took a look inside the door. There was a smaller cross piece and a more substantial bit of framing. So I used the 6mm auger bit and chain drilled through these and then a pad saw to join them up.

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Realising that the bolt holes would be across some of the sections that had no support, I used some of the solid wood removed to make packing for those areas and glued them into place.

Using one side of the porthole as a template I marked up the holes for the bolts. I did a few test fittings at this point and trimmed off any wood that would stop the porthole fitting flush. There were nuts on the coach bolts so I used a step drill to make space for these. And as mentioned above the hole needed to be trimmed with a chisel for the portholes to fit snuggly.

The porthole was removed at this point and the door flipped over. The porthole was pushed back onto place and held in place by hand. The mating face was fitted and a couple of the nuts were added to hold it in place. The rest of the nuts were added and then I went around and tightened them all up. I am hoping that these bolts will be sufficient to make the seal water tight but I do have some frame sealant if that proves not to be the case. The last step was to remount the door and then repeat the whole process with the second door.

By Andy from Workshopshed 2 Comments

  Posted in: Circle Jig