Locating Fender chassis mount holes

[Randall]

Does anyone have a good method for locating the holes for a typical Fender drop down chassis mounting strap bolts? I'm terrified I will get it wrong and mess up my new cab. I was thinking of setting it upside down and placing the chassis, and marking the spots through the chassis holes, and then drilling from the inside, but the spots are so close to the sides, I'm not sure how I would fit a drill in there.

Is there a better method that allows for drilling down from the outside/top?

[nevetslab]

Does anyone have a good method for locating the holes for a typical Fender drop down chassis mounting strap bolts? I'm terrified I will get it wrong and mess up my new cab. I was thinking of setting it upside down and placing the chassis, and marking the spots through the chassis holes, and then drilling from the inside, but the spots are so close to the sides, I'm not sure how I would fit a drill in there.

Is there a better method that allows for drilling down from the outside/top?

I'd make a template. If this is a one-of, you can still be accurate using good cardboard (not box cardboard). I'd use the mounting centers on the chassis for your left-right placement. Get the overall outside width of the cabinet, then the width of the chassis, as there will be some gap on both sides of the chassis so it slides in without binding. Subtract the center-center dimension of the chassis mtg holes from the cabinet width, which will give you the offset from each side of the cabinet. You might want to put blocks on each end of the template, where the overall width of that template would accomodate the block widths, so it would fit tightly over the width of the cabinet.

The front to back dimensions.....I'd use the rear hole centers from an existing cabinet to find the rear holes of your template. Then the front holes would be that dimension you get off of the metal straps' mtg centers. You could also put a block or two on the rear of the template, so it's blocked on the two sides and rear, then using holes small enough to pass your center tap or marking gauge thru, you punch the starting holes into the top, then carefully drill down/thru the top.

You could so something similar that not a permanent reusable template, but you'd go thru the same steps to find the side to side, front to back centers relative to the outside width of the cabinet.

Being a machinist, I have adjustable Machinist squares, calipers, long engineering scales to work with, as I'm always doing some sort of mechanical layout work. And, of course a calculator to keep from counting on my fingers.

[Bill Moore]

I always drill the holes after I assemble the cab.
With the chassis sitting where it should with the correct setback I mark the holes. I then drill a very small hole, (1/16" or so), through cab and tolex. I cut the tolex around that center hole slightly larger than the bolt size you need, and then drill the cab to the correct diameter.

[SoulFetish]

*Assuming the cab is close to square; use the metal mounting brackets as your front to back hole spacing template. Light screw them into place on top of the chassis and measure the distance from the inside edges. This gives you a squared correct mounting template.
Then put the cab upside down and put the chassis in the cab like you were mounting it. Measure from the back of the cab to the closest mounting hole center. Thats all you need. Then center the template left to right on top of the cab and make sure both back mounting holes line up with your measurement. Tape it, centerpunch it, drill it

[Randall]

I went with the template method. The problem here is the holes are in the bottom of the chassis, lots of room to get it wrong trying to mark the holes from the under side. I got some large poster board at the Dollar tree ( two for $1), and cut out a piece the dimensions of the bottom of the chassis. I then cut out a hole large enough to place the cardboard rim onto the chassis, making quite sure the back edge was flush. I taped it all down and found the holes with a pencil and an awl, making nice clean holes. Then I flipped the cab, placed the chassis where I wanted it, and measured a 1" setback from the back of the cab top at the straight edge. Remove chassis, flip cab up right, and place template on top. Using a small square from under the cab top, I measured the same 1" set back from the vertical side of the square to the back edge of the template on both sides. Now using the level as a straight edge from the cab sides, center the cab from side to side, always checking the 1" set back is maintained. Once I was satisfied it was as close as I could hope for, I center punched the four holes and drilled them out to 3/16".

Well, I am happy to report, all four screws dropped right down through the chassis like a charm. The chassis is centered and set back nicely, and I am off on the next adventure!

[Tony Bones]

I just measure. A so-called quilter's ruler makes it super quick and easy. Available at Michaels or online. I have several sizes and depend on them for layout and quick pencil drawings.

[nevetslab]

I went with the template method. The problem here is the holes are in the bottom of the chassis, lots of room to get it wrong trying to mark the holes from the under side. I got some large poster board at the Dollar tree ( two for $1), and cut out a piece the dimensions of the bottom of the chassis. I then cut out a hole large enough to place the cardboard rim onto the chassis, making quite sure the back edge was flush. I taped it all down and found the holes with a pencil and an awl, making nice clean holes. Then I flipped the cab, placed the chassis where I wanted it, and measured a 1" setback from the back of the cab top at the straight edge. Remove chassis, flip cab up right, and place template on top. Using a small square from under the cab top, I measured the same 1" set back from the vertical side of the square to the back edge of the template on both sides. Now using the level as a straight edge from the cab sides, center the cab from side to side, always checking the 1" set back is maintained. Once I was satisfied it was as close as I could hope for, I center punched the four holes and drilled them out to 3/16".

Well, I am happy to report, all four screws dropped right down through the chassis like a charm. The chassis is centered and set back nicely, and I am off on the next adventure!

[ATTACH=CONFIG]53502[/ATTACH][ATTACH=CONFIG]53503[/ATTACH][ATTACH=CONFIG]53504[/ATTACH]

Nice job on the cabinet finger joinery (I assume you did the woodwork)! Love it when transferred dimensions reappear right where they are supposed to!

[Randall]

"Nice job on the cabinet finger joinery (I assume you did the woodwork)!"

No, I cannot take credit for that, I am not a woodworker by any stretch. I had a friend build it, although I did supervise. He did a real nice job, I agree.

[Randall]

Note: I just realized in the photo above with the template on top of the cab, the holes line up, but I have the template reversed front to back. This does not accurately show the rear 1" setback, probably the most important part of this exercise!

[nevetslab]

Note: I just realized in the photo above with the template on top of the cab, the holes line up, but I have the template reversed front to back. This does not accurately show the rear 1" setback, probably the most important part of this exercise!

However, looking at your third photo with the chassis mounted, no baffle installed, it looks like the bottom of the slope WOULD be at the front edge of the baffle/grille cloth. Does it land there?

[Randall]

"However, looking at your third photo with the chassis mounted, no baffle installed, it looks like the bottom of the slope WOULD be at the front edge of the baffle/grille cloth. Does it land there?"

Yes. It was designed so that the chassis and the baffle share 1/4" setback from the front edge, and that is where they are. Pretty happy about that, my first cab and all. Now, if I could just get up the nerve to tolex it.

[SoulFetish]

Ah, when you get to the point of thinking about tolex’in, is when you start realizing that the natural pine finish looks pretty good!

Looks good, Randall! Came together quick nicely