When I had the engine mounts made for my T-Tub, the "bisquits" I used had 1.1" bottom pieces, so I had the holes in them cut to that size. I subsequently used those mounts on my engine test stand, so they are out of the picture. It seems that all of the mounts available need a 1.25" hole, as they are slightly bigger. I have tried to "hog out" the existing holes with a file and a carbide bit in a drill. It is very slow going, and I'd like to find a quicker, easier way. I looked on line, and can't seem to find any large carbides or similar tools (at any kind of a reasonable cost). When I was a kid, my dad had a big reamer he used on plumbing pipes. It chucked into a brace and bit (!?!!), but it would have been perfect for this, but they don't seem to exist anymore. Anybody got any ideas or maybe a source for a reasonably priced tool?
You can stack hole saws. Inner one the size of existing hole , outer one the size needed. Inner holds the outer saw true.
You can buy that step bit (I call it an orange county chopper bit (they never used anything but them)) at harbor freight as well. Cheap, and gets the job done, then you wont feel bad about tossing it before your friends see what you used.
Sometimes you have to close something up in order to open it. What I mean is that you can weld a piece of sheetmetal over the existing hole and then use that sheet metal to start drilling with a larger hole saw.
I weld a piece of junk strap steel across the hole, drill the center and use it as a guide for my hole saw arbor...works every time.Use a compass to find the center of the hole.
Tub Most places that sell machine tools should have an adjustable ream. .125 isn't a lot or doesn't sound like it does it. I have seen step drills that go pretty big maybe one of those will work for you.
Yeah, the raw deal is drilling thicker material than the steps. Then its a bit of a dance to get a hole where you want it the size you want it. I wish I knew how the sharpen one of those rascals.
Looking at the original post, the increase is only .025" Some of the suggestions above won't pilot on a 1.1" hole. I like the correct size drill here. I personally haven't seen a motor mount that was .025" critical.
I like the double hole saw idea as well. I'm going through 3/16" plate, so the $5.99 ones on the bargain table at the hardware probably won't work. If the step drill doesn't work, I'll probably look into the hole saw thing, but I don't think I'll like the cost. I wish they'd made all the mounts in the same size. It's things like this that really slow me down on a project.The mindset I get into when something like this happens is worse than the actual problem.
Yep a 0.025 increase is pretty small. Any carbide burr in a die grinder should make real quick work of it. 0.0125 off the edge.
The double hole saw trick probably won't work with such a small increase. But you could hole saw out a template and clamp/tack to your motor mount. Then use the template as an outer guide for the hole saw
I had mistyped the original dimension, It was 1.25" vs 1.1", which I later corrected. The good current motor mounts have an internally flanged washer that pilots in the hole, so fit is critical, Because of this, I also want the roundest hole I can get, which wouldn't be the case if I ground it out by hand.
I have discovered that the more costly bimetal hole saws work the best on abut anything except wood. The reason I mentioned step drill is that I saw a big one hanging on a friends peg board the other day. I wasn't aware that they came that big until then. I since have seen big ones @ Ace, LOL Ace is the place with the helpful hardware man.
.15 isn't much, scribe the edge of the hole, then a die grinder and carbide but should only take a few minutes and a decent halve round file not much longer. If'n you are somewhat careful, it shouldn't be any less accurate than a hole saw or step bit; maybe even better.
I'll tell you they fit with some slop in every bracket I've seen. I wouldn't stress over machined tolerance there. You don't want a fit like a hot dog in a hallway but I think its really doable.
Just thought I'd mention those step drills don't last very long when you use them on thick metal. I also wouldn't be so critical of tolerance in a motor mount hole. The engine flexes and moves by virtue of the rubber mount anyway. It's not like any critical alignment is necessary.
I've had reasonable luck in thick metal by using them just like a big drill bit. That is, turn them slowly, use cutting fluid or oil, make sure they are straight and don't rock, and don't apply excessive pressure.
Be careful when ordering things from Amazon. I got an email from them today saying my order (the step bit) has been shipped. If you're not vigilant, this may happen to you : Shipment details Latest update: Today 4:06 PM Package received by carrier CHINA Carrier: USPS, Tracking #: LS139926597CN It's a good thing this is a long term project!
You can also drill a hole with the larger size bit thru a piece of wood(say a 1x4) and then clamp the 1x4 over your motor mount and use the wood as a guide.
The Jalopy Journal
