Last month I adapted a gear driven Singer 201-2 so I could use it on a treadle base, but I just now finished the project by installing the belt guard. This was my first time drilling holes in cast iron and tapping holes for screws. It actually wasn’t that difficult, and it felt very empowering.
I bought a bobbin winder from a Singer 201-3 to to use on my converted 201-2. The Singer 201-3 belt guard and bobbin winder assembly attaches to the sewing machine with two screws, which the 201-2 does not have holes for. The holes need to be drilled and tapped for the screws that will be used.
I needed to use a common screw size so I could easily get a tap and drill set to match, so I chose 8-32 screws, which are slightly smaller than the screws used to attach the bobbin winder on the Singer 201-3.
I realized that the heads on most machine screws would be too large to fit into the depression on the belt guard, and somehow I discovered that fillister head screws were what I needed. Most places will only sell you these machine screws in sets of 100, but fortunately I found 2-packs of stainless steel half-inch 8-32 fillister head screws online from Home Depot.
I bought the cheapest tap and drill set I could find, since I only needed it for two holes and I don’t know if I’ll ever use it again. I was very careful with the drill bit and tap, and they worked fine. I discovered my husband already had a tap wrench, so I didn’t have to buy one.
I made a paper template to mark the hole locations, then used a center punch to mark the centers.
I was surprised to learn that cast iron is best drilled at low speed with no lubricant. It’s a good thing I looked that up. The cast iron flakes off as powder, so lubricant just gums things up. I used a vintage hand drill, since I have an easier time drilling straight with a hand drill, and it’s definitely low speed! It took a while to drill the holes, but it wasn’t difficult. I periodically pulled out the drill bit and cleaned off the iron filings.
When I looked up how to tap a hole in metal, I read lots of horror stories of taps breaking and having to be drilled out with diamond bits, so I was extra careful, especially since I was not using high quality tools. Basically, you just turn the tap clockwise until it starts to get hard to turn, back it off a quarter turn or more, then turn it clockwise again. I didn’t use lubricant when tapping the cast iron. I periodically removed the tap completely and brushed it off. The main thing is to never use a lot of force – if the tap starts to bind up, back it off a bit or remove it and clean it.
I put a drop of sewing machine oil on each screw, then installed the belt guard. The screws fit perfectly in my holes.
I put the balance wheel back on, then adjusted the bobbin winder so that the rubber ring presses against the hand wheel when the bobbin winder is engaged. I also had to adjust the position of the bobbin thread tensioner/thread guide on the base of the machine.
Now I can call this project done!