HD28 Kit - First Build

[David L]

Moving right along, nice documentation, keep the pictures coming!

David L

[tippie53]

Martin does use a 1 1/2 degree neck angle . The Martin process is done with a disk . The set it applied to a mold with spreaders . The mold will ride a location post and has stops set into it . This will incorporate the angle into the upper area of the top .
The documentation of my process , which emulates the martin is on your tube in bending video #2. You can use almost anything , as long as you get it close . Ken's method will work also , we just have 2 different techniques of methodology . The key is to be as accurate and to have the process as repeatable as you can .
I was invited out for the first annual Martin Repair Summit . I was allowed to take Photos of the process .

[tippie53]

Using this system which is the same as the Martin procedure , this gets us into the ball bark. I am more concerned of the height at the bridge than the tail and while I use 1/4 inch for a ball park , it gets you close . If I said 1/8 I should have stated 1/4 inch. 1/8 is the max I would want to see at the bridge area
How far you work that 1 1/2 degree angle will also influence the height at the tail . I work the top so I flatten a bit more than the extension . If I can have 1/16 clearance off the finished top at the bridge location that will do the job , but that is a hard line to visualize without the top actual on .
How much of the top are you setting an angle on ? If you look at the photo , the angle is sanded into the soundhole area .

[MuddyFox]

The key to setting up a kit ( yes you may need to trim it ) but before you cut it open the mold and but the sides together and allow the mold to close . You want to see the waist just come up a bit off the mold. You then use the spreader to set the waist against the mold.
The sides will set against the mold tightly. There is a line here so you want to see about 1/8 inch rise off the waist. Watch the side set as you tighten the spreader and you want to see the side set close against the mold sides.

Why is it that we want the waist to come off a mold?
Why would it be bad if the sides were cut exactly to measure and didn't need the waist spreader to conform to the mold?

[Rick S]

The key to setting up a kit ( yes you may need to trim it ) but before you cut it open the mold and but the sides together and allow the mold to close . You want to see the waist just come up a bit off the mold. You then use the spreader to set the waist against the mold.
The sides will set against the mold tightly. There is a line here so you want to see about 1/8 inch rise off the waist. Watch the side set as you tighten the spreader and you want to see the side set close against the mold sides.

Why is it that we want the waist to come off a mold?
Why would it be bad if the sides were cut exactly to measure and didn't need the waist spreader to conform to the mold?

One of the experts should probably answer but I would say that the answer is probably along the lines that (1) it's not possible to bend sides that exactly fit in the mold due to spring back and other issues, or (2) it requires a certain amount of tension for the mold to stay locked in position since the mold is not as wide as the width of the sides and also to force the sides to conform to the exact shape of the mold.

[tippie53]

actually bending gets them pretty close. It is best to allow some trimming . There may be some spring back but not too much to make getting onto a mold too difficult .

[Rick S]

PROBLEM(S) ALERT! - Toward the end of the pre-radiusing process documented above, I noticed that one of my sides had slipped down about an 1/8th of an inch at the neck block seam. It had to be when I was radiusing the top of the rims when the underneath side of the rims at the neck block end were not supported. I didn't think a whole lot about it at the time, I put the sides back in position and continued on to finish the pre-radiusing process and glued in the neck block, tail block and kerf(ing).

After the questions and commentary above about the geometry, I did some more checking and I didn't like what I saw. When I use a straight edge and follow the angle at the top of the neck block, there's no rise at the tail block at all. This I do not understand since the complement neck block angle should be 91 1/2 degrees. Using a straight edge to extend the line established by the contour of the rims at the upper bout, I have one side that shows about a 1/4 inch rise at the tail block but one side only has about 1/16 inch rise.

Any chance that any of this can be corrected?

[David L]

When you repeat your radiusing process with the blocks and lining installed, true rim up in the fixture first and you should be good. I don't think 3/16" is devastating, it should only affect the thickness of the lining on what is now the high side, but by all means wait for some input from some of the more experienced builders, don't want to give you a bum steer.

David L

[MuddyFox]

(2) it requires a certain amount of tension for the mold to stay locked in position since the mold is not a wide as the width of the sides and also to force the sides to conform to the exact shape of the mold.

@Rick, John
I can always make it conform to the mold, but why use brute force in the first place? The questions are:
1) why align side ends and have the waist pop out instead of say using a waist spreader, then bouts spreaders and then cut the ends to measure?
2) why introduce a force that needs to be counteracted by a spreader to conform sides to mold?

[Rick S]

(2) it requires a certain amount of tension for the mold to stay locked in position since the mold is not a wide as the width of the sides and also to force the sides to conform to the exact shape of the mold.

@Rick, John
I can always make it conform to the mold, but why use brute force in the first place? The questions are:
1) why align side ends and have the waist pop out instead of say using a waist spreader, then bouts spreaders and then cut the ends to measure?
2) why introduce a force that needs to be counteracted by a spreader to conform sides to mold?

Muddy, the method that John recommended seems much more simple than what you're describing. I initially tried a similar process with multiple clamps in addition to the waist spreader and then marking the sides at the tail to cut to measure. But I didn't cut just yet. I tried John's method and found that I needed to cut off less than what I would have if I cut to measure. By cutting off less, I ended up with the sides fitting tighter in the mold and I could achieve this with only the waist spreader.

The pop out at the waist is just a guide as to how much tension will be applied when the waist spreader is tightened. Seems like a great system to me.