Questions about using mega mold for contouring back rim

[Jerry_C]

Dear All,
I am a first time builder using KMG mega mold. It has been really fun building this kit.
Currently, I am working on contouring the back rims and I have run into some confusing situation.
I am not sure what I have done wrong and I would like to ask for your advice and comments.

PS, I took these photos after I have already tried contouring the blocks and the rims.

First, I installed the spindle at the center of the body.
Then I use the height adjuster screws on the mega mold to raise the neck block side of the mega mold base.
After raising it, the height of the rim around the tail block and the neck block are leveled.


Then I flipped the abrasive bar. The 15' radius bar is in contact with the rim at the tail block side, but the bar is not in contact with the rim at the neck block side.

I could see a gap between the abrasive bar and the rim.

I am not sure what I have done wrong in this process. I am certain that I have not removed too much material, because I have not sanded to the original profiled side yet.

What would you recommend me to do? Should I raise the mega mold at the neck block side even more?

Another question is:
I have observed that when I rotate the abrasive bar to sand the rims, the whole bar does raise up as I rotate it.
I am not sure whether I can explain this clearly.
As I rotate the bar, the position/height of the whole bar keeps raising up and coming down.
Is this what it is supposed to be?

Thank you so much in advance.
Jerry

[Dave Bagwill]

Hi Jerry - looks like a fine job so far.

Are you 100% positive you did use the 15' radius bar on the blocks?

[Jerry_C]

Hi Jerry - looks like a fine job so far.

Are you 100% positive you did use the 15' radius bar on the blocks?

Thank you Dave.

And yes, I first copied the line from the 15' radius bar, then used a block plane to shave off most of the material, then used the 15'radius sanding bar to sand the blocks. However, somehow, after sanding for a long time, I could never reach to the actual rim material.
So, I tried to reset the height of the blocks. And that is when I saw the gap.

I thought maybe I should try raising the neck block height more until it touches the radius bar. Now it looks like this:

Do you guys think it is ok to carry on like this?


By the way, is it normal to see the radius bar going up and down while rotating along the back side of the rim?
Thank you again.

[ken cierp]

Yeah -- you got something out of whack.

Have you beveled the the waist curve area?

Yes the bar will seek its own level as you work. Looks like you were pressing too hard when doing the neck block area -- titling the post and the bar, plus likely the rim is wobbling in the mold your clamping set up looks unusual? If you drew lines on the blocks as instructed -- why did you sand beyond the lines you marked?

Yes you need to raise the neck block end -- work with control (look at your progress) you should see material progressively being remove. Looks like nothing has been shaved off the upper bout curves. The rim gets beveled all the way around. Now that you have over sanded the neck block additional material will have to be removed to even out the rest of the rim much more work than normal -- proceed with caution, its most important to understand what you are trying to accomplish. When complete the rim will accept the dome shape of the back plate.

[Jerry_C]

Hi Ken,
Thank you for the comments. I have fixed the pictures. Hopefully this is better.

I haven't worked on the upper bout curve and the waist curve area much yet, since I was still having trouble around the tail and neck blocks area.
I am still not too sure why this has happened.

At this moment, I am guessing that this has happened because my kerfing was glued too proud. (about 1/16" proud of the rim).
So, when I adjust the neck block height, the flat side of the abrasive bar was laying on top of the kerfing at both end of the body. Therefore, the contour line I drew on the blocks were probably too high as well. It took me a while to remove neck/tail block materials, way passed the line. And now the heights of the tail/neck block at edge glued to the rims are finally closed to the actual rim heights.

Do you think I have already removed too much neck block material? I examined the rims all around. I haven't even sanded to the actual rim material yet. So far, only the kerfing material (and block material) have been sanded away..

Am I still ok? I hope I am not messing up the rim profile.

Thank you

[ken cierp]

What happened to your preliminary markings/ guidelines? Did you skip that step? Its difficult to get a sense of how much you over sanded.

[ken cierp]

Is there a 1.5 degree slope on the neck block?