Celtic Knot and Scallops

[Souths1der]

The main point of this post is to get some feedback on the Celtic Knot because it was a failure. It may end up being a lengthy post because I'm going to try and be as detailed as possible to find out where I may have went wrong. I have some ideas, but I'm not sure which is the most likely culprit.

I attempted my first two segmented blanks, both for Triton pens (one rollerball, one fountain). They are to be a high school graduation gift to a family friend whose son was accepted and will be attending Notre Dame in the fall (he is also valedictorian of his high school). With Notre Dame as the theme I was using non-stabilized box elder burl double dyed green/gold as the main blank and the Mark Gisi accent sheets for the segmentation.

The blanks were: Celtic Knot the 6 knot variety; scallops.

So far the scallops is successful, I have drilled and tubed it and it is still solid. The blank is the non-stabilized box elder burl dyed green/gold. I used stabilized box elder burl dyed gold for the scallops and the black segment sheets in between. Liberal amounts of thin CA was used for the glue up. Belt sander was used in between scallops to clean up the edges. I let the blank sit 2 days before drilling. I duct taped around the blank before drilling as some have suggested. I step drilled on the lathe starting with 7mm, then 10.5mm, then 12.5 for the cap section. I would drill 2-3 cranks on the quill and then back it out and let it sit for 5 minutes to cool. Then 2-3 cranks again, repeated until through. Used Epoxy for the tubes, and I hope it will turn just fine with light cuts etc.

For the Celtic knot I used the non-stabilized box elder burl dyed green/gold. For the knot I used 2 layers of White/Green accent sheet laminated together with thin CA to make a White/Green/White pattern. I turned the blank round on my lathe. I then used my table saw and a jig to make the cuts at 45 degrees. I left the height of my blade about 1/8" short on the blank so I didn't cut all the way through. I used 5 minute epoxy to put the segment strips in the kerf on the blank. I let that sit for 30 minutes and then put it on the lathe to turn off the excess. Repeated that process for the remaining 5 cuts. The blank looked great, proper separation of the knots, all in line. I was ecstatic. I let the blank sit for 2 days before drilling using the same step process I used for the scallop blank.....

The Celtic knot blew apart on the second drill step 10.5mm. But as I took off the tape I noticed it really separated at the first 7mm step I just didn't see it because the tape held it together but the epoxy bond was broken. So basically the blank broke into three pieces with the entire knot being one of the pieces. The knot itself held together, it's this perfect little chunk of Celtic Knot.

I think maybe I shouldn't have used epoxy for the knot segments, but that's based on the fact that the scalloped blank worked and I used CA for it. I chose to use epoxy because I thought it would be a stronger bond. I also think it could have been the dyed burl wood and that maybe since that is not a very stable wood to begin with, maybe expecting something to adhere to it like a Celtic knot is not realistic. Could be the combination of all three (epoxy, burl, dye) was just a disaster waiting to happen.

I am encouraged though because I think I did the entire process for the knot pretty well, the knot looked great before the drilling. I'm about 5 months into this pen making journey and I hope some of you more seasoned veterans can give me some insight. Thanks.

 

[D.Oliver]

Hey Keith what speed were you drilling at? Also are your drill bits really sharp? Could have the bonds failed because of heat build up?

 

[Souths1der]

I was drilling at 250, slowest speed on my lathe. I believe my bits are sharp, I just bought all brand new hss twist bits, I had been using brad points but switched to twist when I changed form drilling on my drill press to drilling on the lathe.

Each time I backed the bit out after a couple cranks on the quill I touched it to see if it was hot, it never really even got warm. I waited 5 minutes before the next couple cranks anyway. Hole was pretty clean, no visiable signs of a dull bit.

 

[jmm666]

For gluing of the laminated pieces, I would suggest thick CA instead of thin. Then, inserting these pieces into the kerf of the blank requires COMPLETE coverage of glue.

The crisscross of the knot results in some very small pieces within the knot. As the blank is drilled, the stress and heat build up puts the glued joints to an extreme test. In your case, it sounds like the problem was in the glued segments of the knot because the whole knot broke free. Check your process when inserting these pieces into the kerf to ensure there is complete coverage on both sides.
It sounds like you were careful with every part of the process and it's frustrating when it still fails.
One other thing is that burls are not the easiest blanks to use for segmenting because they don't have a consistent grain direction and glueing is even more critical.

Good luck
John

 

[Krash]

Hey Keith,

I feel your pain. I had the same issue, trying to step drill with limited success. So, I also posted to this great forum and got an answer that was counter intuitive to my tool mind.

Check out Ed's response in my thread:

http://www.penturners.org/forum/f56/drilling-largest-diameter-holes-suggestions-126178/

This approach works wonderfully and I haven't had a blowup since. I don't even have to step-drill it anymore. It works for segmented material that has a dramatic difference in hardness from the wood around it or on very hard wood like ebony. Take a spare bit and give it a go.

 

[jttheclockman]

Hello Kieth

Welcome to the site and welcome to the world where things go round and wrong. 5 months and attempting this. I hope other people are reading that for various reasons on here.

As to your problem. As you say it could be a combination of problems. My opinion would be the wood choice to start with. Not the strongest of woods to hold together when stressed and you will be stressing it. But there maybe a way around that too. Now from what you stated and thank for the detailed description because it helps. To me it is in the glue choice of the segments to the blank. When you glued the layered sheets together, you used thin CA and that is good. Why because it is a complete surface to surface match. The same goes for when doing scallops because you are gluing pieces together and the mating surface is clean and flat.

Now what happens when you glued the segmented strips into the kerfs for the knot, they may have been just a tad bit undersized and thus some gaps are left and probably are not even visible to the naked eye. The choice of epoxy to me is a good one. Some people have had good success with thick CA or even med CA. Do not use thin CA in this case. As per all glues there are dry times and cure times and vary from glue to glue and temp. to temp. Age of glue and open time are factors when using also. I am not a fan of 5 minute epoxies. They do not stay as flexible as other epoxies. They break down at a lower temp rating also. So you have to be careful when drilling to not get too heated.

Now drilling. When drilling the step method is a good one and sharp bits are a must. Reinforcing the outside of the blank is good also even though duct tape would not be my choice. I prefer if it is round blank some gauze soaked in CA. But after drilling each hole I would coat the inside of the hole with thin CA to help stabilize the blank somewhat. This is what I meant when I said you maybe able to use the blank material you want. Do the CA trick after each drill bit and make sure it is dried before drilling

I like to adhere my tubes to the blanks with epoxy because of the above mention of the gaps.

Not much more I can say but good luck. There will always be failures and that is the frustrating part of segmenting.

 

[Souths1der]

Thanks for all the ideas guys. To answer some of the questions:

I thought I did a good job as far as epoxy coverage in the kerfs. I used a flat toothpick to spread it all over on the inside of the kerf and then spread some on the segment material directly. I moved the material back/forth and up/down all over to spread it around when I put it in the kerf. I then used the leftover epoxy I had mixed and spread it over the external joint. However, now that I'm thinking about it, I did not blow out any dust from the kerf. The segment material was also not extremely tight when I did a dry fit. With the epoxy in place it was tight but I did not have to force it in the kerf.

I used 5 minute epoxy because that is what I have on hand for tube glue ups. I'll go out and get some 15 minute to be more versatile. I have a very bad habit of just using what I have on hand and not being patient and getting exactly what is needed. I'm working on those shortcomings though, I waited a whole 2 days to drill these blanks!

Duct tape...again, bad habit, it's just what I have on hand. I didn't have any packing tape, honestly that was my first choice based on the things I read when I researched. Didn't know about soaking gauze in CA. I think that may be what I do in the future.

 

[D.Oliver]

Well it sounds like you did most things right, but sometimes you can do everything right and have it still not work out, other times it seems like you can do everything wrong and still make it work. Hopefully the next ones works out for you.