That was how we did our first 98mm bore, when we went to a 75mm bore, my hand was too big to get a dremel in and cut out the scrap... so we went to nesting. You can pick up cheaper hole saws, don't bother with the Bi-Metal expensive ones.
Erik Gates
I promised I would report back after making the modification to my Ultimate
> Endeavor so here goes....
>
> The original plan was to convert my 54mm motor rocket to a 76mm motor mount.
> Erik Gates offered a suggestion (below) and I set out to give it a try. My
> first trip to Home Depot revealed that a hole saw sized for a 76mm tube was
> out of the question. 3" was too small and 3.25" too big. Besides this each
> hole saw was $15! I left disappointed.
>
> Thought about it some more and remembered the suggestion to just go for 98mm
> and adapt down to 76. The 4inch hole saw would work very well for this.
> Unfortunately Erik's suggestion to nest a bunch of these saws and get the
> extenders to reach into the rocket was out of my price range. It would have
> cost over $100 so I looked for alternatives. I ended up buying some 1/2 inch
> threaded rod and some nuts and washers along with the 4" saw. I turned a
> small 54mm disk in scrap aluminum and bolted it to the rod in front of the
> hole saw to act as a guide as it traveled up the motor tube. This would
> still require me to stop every couple inches and Dremel out the parts but it
> was cheap!
>
> The good news is that the finished job is perfect. A clean hole through
> three 1/2 inch centering rings and 6 G-10 fins. Eyeballing down the length
> of the fins shows that the line is dead straight. Bad new is it was messy
> business. Lots of bad smoke, cutting with the dremel cut off wheel deep in
> the rocket and I was sure I would smash the rocket every step of the way.
> Knuckles are a bit sore but it is done. If the rocket had been a
> conventional 3 fin rocket I would recommend this process to anyone as "the
> first 6 inches" were relatively easy. It was the long forward fins that
> really were the most difficult.
>
> Thanks for all the suggestions,
>
> Stuart Leslie
>
> > > Buy a 54mm Hole saw and grind down the teeth so it will be just a guide.
> > > Buy hole saws that will nest all the way up to the 75mm size you want,
> > > actually you need to bore it out to about 78mm (the outside dia of the > > 75mm
> > > motor tube) Use the holes in the hole saws or drill your own and bolt > > them
> > > together. Put a couple of nuts in-between the 54mm and the rest so it
> > > sticks out in front, this will be your guide. Use drill extensions and
> > bore
> > > it out! Wrap the booster in blankets, and strap it down, it wants to > > spin!
> > > Use a Aeropack retainer, it bolts to the bottom bulkplate, and the motor
> > > tube is just a guide, the retainer will be you thrust plate as well.We > > bored
> > > out some of our earlier rockets, and have learned to just make the motor
> > > mounts as large as possible, you can always adapt down! Why make it > > 75mm...
> > > go to 98mm, or you will be boring it out again next year! :-) > > >
> > > Erik Gates
> > > Gates Brothers Rocketry
> > >
> > > P.S. The reason you nest the hole saws, is if you just use 54mm and a > 78mm
> > > hole saw, every 2", the depth of the cut, you have to go in with a > dremel
> > > and cut out the 54mm tube and fins to allow the hole saw to keep > cutting.
> > > If you nest the saws they chew up all the material and allow you to bore
> > > continuously. Just have a vacuum close by, it makes a mess! > > >
> > > > Anybody tried to convert a rocket from a 54mm motor mount to a 76mm > > after
> > > > the rocket is built?
> > > >
> > > > I built my PML Ultimate Endeavor intending to use it for my Level 2 > last
> > > > year but ended up using a smaller rocket with a J350 based on motor
> > > > availability. Now I am mostly just flying sugar motors (a lot cheaper
> > for
> > > > certain!) but my AMW 54mm casing will only get me up to a full "J" > motor
> > > > with sugar. I am building some 76mm hardware and would like to > > reconfigure
> > > > the rocket to a 76mm mount. The endeavor has two sets of fins at the > > > bottom
> > > > and they are quite large. Looks like a lot of tricky dremel work to > me!
> > > Not
> > > > too mention the 3 half inch thick centering rings already installed. > > > >
> > > > Anybody do this kind of operation before? Any tips? Should I bother? > > > >
> > > > Thanks,
> > > >
> > > > Stuart Leslie
> > > >
> > > >
> > >
> > >
> >
> >
>
>