Dreaded sandthrough

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Tiger

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The last few pens I've made I've managed to sand through my CA finish, it's often just a small spot but nevertheless it means I've got to re-do the CA finish and sometimes even after a few coats of CA the same spot will return and I'll need to do a third application. Are there early clues to the sandthrough as I'll often discover it in the final stages of the process after already investing a fair amount of time on the pen? I should say that after putting on my CA I start sanding at no less than 600 grit but often at 800/1200 and use a light touch. I put on 6 to 10 coats of thin and 1 to 3 coats of medium adjusting based on digital caliper readings.
 
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I'm sure most of us have had this happen. It sounds like your barrel may be ou of round. If you are using a mandrel, it may have been over tightened. (IF it IS indeed out of round) For your CA application, try 2 coats of THIN, and 6 coats of MEDIUM. Continue sanding with light pressure. Hope this helps.
 
I have done that many times with "perfectly" round and slightly OOR barrels. I am not sure if that is the your case. The only way that I stopped it (at least until it happens again :-) ) was practice/experience. I try applying the CA with very smoothly coats and ensure that I coat the the ends (extremes; not the vertical ends) with the same amount of CA. If the coats are smooth (no ridges,etc.), I don't need to sand as much. I also start sanding with the least aggressive grit first. I stopped wet sanding and use buffers, but I even buffed-through some barrels. This was not a great response to your question; I am just sharing my experience. Happy finishing!

PS. I use 2 coats of thin and 8 to 10 coats of medium (but not heavy coats). Some say they can get away with less; I cannot.
 
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What brand of CA are you using? I used BSI thin/med for about a year and didn't have many troubles sanding through. Switched to Mercury Flex thin and now fight it on nearly every pen. I think the flex is softer and more prone to this issue. Just my experience...
 
I believe I mentioned this tip to you before in another thread. But it is a good reminder. When sanding especially with sandpaper that has a course grit like 400 or 600 it is always a good idea to back the sandpaper up with a small block of wood. When you sand with your finger tips, they are soft and possible put more pressure on an area than others. Maybe because the way your hand follows the contour of the blank or whatever. But with a block of wood it is the same over the entire blank. Doing a CA finish becomes easier the more you do and you learn from mistakes as you go. Good luck and keep at it.
 
If the sand through id on the horizontal, make that spot on the mandrel. if if's in the same spot every time,I'd say the mandrel is bent.

I had sand through on a few pens and learned with a smooth and even CA finish, there is no need to use a lot of pressure.
 
John T. has a good idea of backing up the sandpaper. I find the sanding sponges in fine from HF do a good job of getting the ball rolling in the last stages of finishing. I sand from side to side with them, BTW. Then I go through the sanding pack of grits.
 
Thanks for the replies, I appreciate them. Just to reiterate the point of the thread it's more about how one can get some feedback during the finishing that they have got enough CA on that they don't have to start again as I often find out when I'm well into the process that I've got sandthrough.
The CA I use is the same that I've always used, I do use a small wood block behind the sandpaper and I start sanding at typically 800 or 1200 grit, I do try and use as little pressure as possible but I guess that's a subjective call.
I have a small horizontal misalignment on my Jet mini lathe which may or may not cause some OOR but I have in the past had less issues with sandthrough.
 
Tiger said:
Thanks for the replies, I appreciate them. Just to reiterate the point of the thread it's more about how one can get some feedback during the finishing that they have got enough CA on that they don't have to start again as I often find out when I'm well into the process that I've got sandthrough.
The CA I use is the same that I've always used, I do use a small wood block behind the sandpaper and I start sanding at typically 800 or 1200 grit, I do try and use as little pressure as possible but I guess that's a subjective call.
I have a small horizontal misalignment on my Jet mini lathe which may or may not cause some OOR but I have in the past had less issues with sandthrough.
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I will say use 3 coats of thin and more med. It is a matter of feel over time. No one clue is going to tell you you sanded through or about to. If sanding evenly and there are no dips in the blank then should not happen. Should not have to sand much at all off before going to polishing stages. If so then you either put too much CA on or your technique is off. Checking with calipers is key and know just about how far over before polishing out you need to be. It really is a feel thing. Have no other answers for you. Sorry.
 
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