Bridge Conversion - 3-Hole 6-Saddle Top-Mount to 3-Saddle Glendale String-Through

[radio]

Finally, after a lot of great input from my fellow Forum members, I did the "deed" last weekend. It will take me a while to get the pictures linked, but here we go:

This is the stock configuration - nice sustain, with some passable twang and thunk, great for blues and jazz, too:




OK, here's the result of using the drill press before making sure the drill bore is perpendicular to the work surface. My grandfather purchased this old Buffalo Forge sometime in the 1930's, and it is really solid - just in need of a tune-up. You'll see that without the locator pin which jwells suggested in his thread, the bit comes through at an angle, so even though the bit doesn't wander, it's still messy. Dale (Glendale) suggested that I drill straight through from the front on all holes; later, you'll see why I'm glad I didn't. One other suggestion by jwells was to only drill the outside 'E's" through, and use them as an alignment guide; it has merit.




This is even worse (Thank God, I decided to use a practice piece): The string-through ferrules have a body diameter that requires 5/16 inch bit; the flange on the ferrule, if you want to countersink it, (I did) requires 3/8 inch. This shows what happens when I aligned the bore with the 3/16 inch bit I used for the string-through holes - not very precise. The counterbores for the ferrules are off-center from the string-through holes; the result is that the ferrules were tilted in the holes, and wouldn't seat all the way - this is a disaster even if you don't want to sink the flanges into the back of the guitar.




Here's the finished project. This is still great for jazz, but it is now an official Twanker!



Only four images per post, so I'll Continue in Part II
Next: Squaring up the table on the drill press

[indiobravo]

looks great, radio :-)

just a quick comment on the "some passable twang" - i have the exact same original set up - top loader, three screw in my 94 mim. It has more twang than my two other string-thrus. just wondering if anyone else has the same experience.

(i still wish it was string-thru, but only because it's what i am used to on my other guitars)

[boris bubbanov]

Glendales!

Nice alignment. Congrats.

[radio]

Originally Posted by indiobravo

looks great, radio :-)

just a quick comment on the "some passable twang" - i have the exact same original set up - top loader, three screw in my 94 mim. It has more twang than my two other string-thrus. just wondering if anyone else has the same experience.

(i still wish it was string-thru, but only because it's what i am used to on my other guitars)

Thanks, indiobravo. I changed the neck pup to a DiMarzio Twang King, and that really made it sing, especially in the middle switch position. It's subjective, of course, but I was happy with the stock set-up, and if I get another 90's MIM, I'll keep it as top-load - just a different sound.

[radio]

OK, second part now. I'm sorry about the delay, but work, school, practice . . .

The old drill press I had seemed pretty rock solid, but just on a lark, I laid a 6 inch carpenter's square between a drill bit and the 3/4 inch MDF work table I made to protect the guitar from the tool rest (metal table), and guess what? There was a gap when I checked front to back (but not side to side! This meant that the work table and tool rest upon which it lies was sloped, with the front slightly lower than the back, and that any holes I drilled through wouldn't be perpendicular to the plane of the guitar. NOTE: If all I cared about was having 6 holes all in a row, then I wouldn't have to go through this little bit of trouble, BUT, I'd have to align the guitar body exactly the same for each hole. Also, I couldn't use the locator pin (In Part III) to center the counterbores for the ferrule flanges - they wouldn't line up. This seemd to relieve just another set of worries, so on we go!

In this first picture, there is no gap: (That Small Hole At The Square Under The Bit Will Be For The Locator Pin)




Here's where the problem is:
Gap Is 0.007 Inches


OK, I know the gap and the height of the bit from the top of the square to the tip, and the same angle is created from the plane of the existing work table to the correct perpendicular position:

Math for Table Shim:


So I had some old rubber mat, the kind they used to use to cover architect's drawing tables; it's just about 0.040 inches thick, and it doesn't compress much. I cut a strip as long as the table and about 1/2 inch wide. You can see it at the front edge between the metal tool rest and the MDF work table:




Re-checking the gap, I can't get the 0.0015 inch feeler gauge behind the bit.


Part III in a few days . . .

[boris bubbanov]

Cool. Nice post.

Yeah, I know that mat stuff, green on one side, beige on the other. Always been around, never thought to use it for that, though.

Now, what to do about run out in the actual drill press itself?

And when are the powers that be gonna come out with speed steel drill bits with more steel and less discharge "ports" or whatever you call them. I can go slow; I just want a truer bore with less wandering. Is that really too much to ask for?

[radio]

Thanks, Boris. The drill press does have a little run-out, but short of changing the bearings, I don't know how to correct for any wobble; I just accepted any eccentricity in the hole to be included in all the holes - some uniformity, anyway. My state (CT) is chock-full of machinists and tool and die experts, who would know what is acceptable, and what needs attention - I'm not one of them, unfortunately! I have seen experts take an old, worn-out tool, and convert it to a specific purpose, where its failings were acceptable - kind of like Clapton picking up a $30 beach guitar and getting more music out of it than would seem possible.

I suspect that the logical conclusion to better bits would be end mills, used for denser materials (metals), which have a lot more cutter than chip clearance slots. Maybe an end mill for wood, with vertical cutters?? There's your fortune, buddy, get busy!

[radio]

Here's the new Glendale bridge laid over the three mounting holes. As you can see, the new mounting screws (on the bottom on the ruler) are larger than the stock (above).




With a soft wood, I might not have needed to use the proper clearance drill, but I decided to just twirl the correct bit in the holes by hand:



A cigar awl works perfectly to mark the holes; its thin enough that I can look from two directions to line up the exact center:



The positions are marked, so in the next installment, I remove the rest of the hardware and the neck from the body, and go nuts a with power tool. BTW, I found a thin, clear/white plastic shim under the bridge end of the neck pocket - I'll re-install it, but I wonder if it need it, since I'm using 0.011-0.050 strings, which are heavier than what the guitar came set up for - another post sometime . . .

[radio]

Now, I'm going to drill from the back of the guitar, so I align the bit with the locator pin, and I check it for each hole I drill, cleaning the dust and chips away each time - Thanks, jwells! Each hole I drilled from the front will fit onto the pin, and when I drill from the back, the holes should meet. When you do the alignment, make sure that the travel of the bit won't meet the pin, it will destroy the bit. I practiced on my piece of wood with all three bits, and it looked pretty good - all holes nice and concentric. Make sure that the locator pin doesn't wobble; when you drill the hole for it, let it be a snug press fit, and make sure that it is long enough that the guitar body won't wobble because it doesn't go far enough into the body - my pin is 1-1/8 inches long, 1/2 inch is in the work table and 5/8 inch projects into the guitar body. If I ever do this again, I'll have the pin extend through the work table, but still be able to pull it out, so I can use the work table for other operations. 5/8 inch into the guitar body seems like enough.





Securely clamped. The gold bit was a regular metal-working bit I used for my test holes; I intend to use the nice new Forstner (brad-point) bits I just bought for the real thing.




Almost done on this side




My one mistake, which will be covered by the larger bore of the countersink bits for the ferrules, was that I let the bit poke through from the front too far. You can see on the first three holes that it chipped off the thick finish. I didn't have to let the bit even penetrate the surface of the back of the guitar, since I know that the holes will align. See the three "pinholes" holes for the E-A-D strings? That's all that's needed.

[radio]

Measure the depth of the whole ferrule, then add the amount you want the ferrule to be below the surface of the guitar body. The ferrule OA length is 0.307 inches; the body (5/16 inch diameter) is 0.25 inches long; the flange (3/8 inch diameter) is 0.057 inches long (note that 1/16 inch = 0.06125 inches!). (Check the math: 0.250 + 0.057 = 0.307). Not to split hairs, I just used something measurable on my drill press, so I used 3/8 inch = 0.375 as the overall depth of the hole; the flange will just sit below the body of the guitar.

I chose to countersink the whole ferrule




With the first hole in the front of the guitar positioned on the locator pin, and the cutting edge of the 5/16 (ferrule body size) bit just in contact with the body, meaning the brad point of the bit is inside the hole, I measure the distance I want the bit to travel from this point on, which I have determined to be 3/8 inch. I set the limit stop (knurled adjustment nut) to this.




If you want the top flange to stand proud of the body, then only measure the depth that will protrude into the body (0.25 inch). You could drill more than you need, in this case, and the top flange would keep the ferrule from entering the body, but there are two reasons not to do this: 1.) You want the bottom of the ferrule, the part that meets the body inside the hole to be in tight contact, and 2.) The difference between the diameter of the ferrule body and the flange is very small, 3/8-5/16 = 0.3750-0.3125 = 0.0625 inches, which isn't a lot in soft material - the flange could be pulled into the body by string pressure.




There! The practice piece (bottom hole) shows pretty near concentric bores for the string hole, the ferrule body and the ferrule flange. Also, the ferrule was a snug fit in this hole, with the flange just below the surface. If you do this, use something softer than aluminum and brass to drive the ferrule back out - don't want any imperfections to cause string breakage, so we?

[radio]

I chose to start with the larger 3/8 bit first. That way, I only had to cut (stress) the guitar finish once; the smaller 5/16 hole would be inside the 3/8 hole. I ended up using 1/8 inch (0.125) for the depth of the flange hole, since 0.058 was too hard to measure.

Remember, after each operation, lift the body off the work table (carefully, or you'll scratch the body against the drill bit), and clean the dust/chips off the guitar body and the work table. We were shimming the work surface for 0.040 inch, and that dust can throw our measurements off easily.




3/8 ferrule flange holes finished; now for the 5/16 ferrule body holes. Depth of hole will be 0.375 inches. Theoretically, the ferrule will bottom out and meet the guitar body solidly, but the flange will not. I don't expect to lose anything in the string-to-body contact this way. As is is, the string-through holes are 3/16, and they may not even hit the side of the holes in the guitar body - probably just the ball end pulling on the ferrule, and then the edge of the bridgeplate before running over the saddles.




Almost done -




Finished with this part. My only regret was that I couldn't chamfer the edges of the holes, as jwells393 showed in his post, but I was afraid of disturbing the finish too much.

All that's left is to remount the hardware, string 'er up, intonate and start twanging.

My next project may involve nut business




Thanks to all the helpful posts I found on this forum by jwells393, boris bubbanov, and others, whose posts I have misplaced - sorry.

Separately, I'd like to say that the workmanship of the Glendale product was very good. Two exceptions: the glass-beading of the chrome plating on the inside vertical surface of the bridge plate was not uniform, but it's not noticeable; the screw holes for the bridge mounting screws needed reaming - they appear to be the correct screws, but the body wouldn't go through without hand-reaming the plating off the hole - nice tight tolerances! The saddles and ferrules are very well made.

I'm glad I did the conversion.

[jwells393]

Why are you starting a new thread for each step? Just post replies in your original post. This is hard to follow.

How about cleaning this up ............ putting everthing in one thread, delete the post in the others and let them fade into oblivion.

[radio]

Originally Posted by jwells393

Why are you starting a new thread for each step? Just post replies in your original post. This is hard to follow.

How about cleaning this up ............ putting everthing in one thread, delete the post in the others and let them fade into oblivion.

Sorry you're having trouble; I split it up so that the pictures could be posted, and the forum only allows four pics per post. I figured that the pics might be helpful, but I could just condense the whole thing.

[jwells393]

That's four pictures per post ............. not four pictures per thread. This is a post. The entire subject is a thread. You can have an unlimited number of pictures in your thread ............. four at a time.

Look at any build thread ......... the originator will have dozens of pictures. Look at Buckocaster51's behemoth build thread. He's posted hundreds of pictures in it.

If everyone created a new thread for each group of four pictures, the forum would be a complete disaster.

[62_Inca_Esquire]

Originally Posted by jwells393

That's four pictures per post ............. not four pictures per thread. This is a post. The entire subject is a thread. You can have an unlimited number of pictures in your thread ............. four at a time.

Look at any build thread ......... the originator will have dozens of pictures. Look at Buckocaster51's behemoth build thread. He's posted hundreds of pictures in it.

If everyone created a new thread for each group of four pictures, the forum would be a complete disaster.

+1

I'm sure it was a simple misunderstanding, but these should definitely be compiled into one thread.

[jwells393]

Yes just a misunderstanding. There's excellent information there with great photographs. It would just be much easier to follow if it was all in one thread.

[J-man]

Fixed.

[radio]

Thanks for consolidating, Jman. The edit feature was turned off for me. The only one missing now is the first one from April 11, called "Bridge Conversion - 3-Hole 6-Saddle Top-Mount to 3-Saddle Glendale String-Through"

Sorry to the other forum members for the inconvenience.

Steve

[jwells393]

Did you fix it J-man .... if so ......... Good job.......

[J-man]

Originally Posted by radio

The only one missing now is the first one from April 11, called "Bridge Conversion - 3-Hole 6-Saddle Top-Mount to 3-Saddle Glendale String-Through"

Done.

[boris bubbanov]

Originally Posted by J-man

Done.

Thank you, kind sir!