Need 1/8 blade for incremental box joint jig ??

[Benjimin Young]

I had a fun weekend building an increment box joint jig that relies on a threaded rod 16 tpi so 2 turns = 1/8. https://www.youtube.com/watch?v=JYxDXHGRRrk
I am now on a quest to buy a good 8" or 10" 1/8" blade that will prodice a good flat bottom finish but minimize tear out. .125 kerf FTG. I see there are box joint sets that do 1/4" and 3/8" but they are pricy.

Thoughts? Suggestions?

box joint jig1.jpgbok joint jig2.jpg

[John TenEyck]

Why not just use a good quality, full kerf ripping blade? You may have to get it resharpened to be exactly 0.125" width, but that doesn't cost much. This Freud is really close at 0.126" kerf: http://www.freudtools.com/index.php/...oduct/LM72M010 You need a backer board to prevent tearout so as long as the blade you choose cuts smoothly it should work fine.

John

[Lee Schierer]

The Freud LU84M010 has 50 teeth arranged in groups of five, each of which includes one flat-top raker tooth for fast, accurate ripping. Each flat tooth is followed by four alternating-top-bevel (ATB) teeth that are particularly well suited to crosscutting, and large gullets between the teeth ensure effective chip clearance. The kerf is .126, which should be ideal for your box joints. Remember a 1/8" finger will not fit in a 1/8" slot, you need a slight amount of clearance.

[Cary Falk]

The Freud LU84M010 has 50 teeth arranged in groups of five, each of which includes one flat-top raker tooth for fast, accurate ripping. Each flat tooth is followed by four alternating-top-bevel (ATB) teeth that are particularly well suited to crosscutting, and large gullets between the teeth ensure effective chip clearance. The kerf is .126, which should be ideal for your box joints. Remember a 1/8" finger will not fit in a 1/8" slot, you need a slight amount of clearance.

All the teeth need to have a FTG or you will get lines from the ATB teeth. Any full kerf FTG will work. You will probably need a backer board because of the lesser number of teeth.

[glenn bradley]

Plenty out there:

20 Tooth -

http://www.carbideprocessors.com/saf...ds-best-37376/

24 Tooth -

http://www.carbideprocessors.com/wor...ip-saw-blades/

[glenn bradley]

On the cheaper side:

https://www.amazon.com/Freud-Tooth-P.../dp/B0000225UD

[scott spencer]

ATB/R and TCG won't leave a truly flat bottom because the non-flat teeth protrude above the flat raker teeth. A flat top grind (FTG) is the only grind that will leave a truly flat kerf. Those are mainly rip blades like the Freud LM72, Infinity 010-024, CMT 210.024.10 in the $50-$60 range. For less money, the Delta Industrial 35-611 is made in Germany by Leitz, and should do an admirable job for ~ $30 to your door.

[glenn bradley]

Thanks Scott!!! I corrected the links.

[Dick Mahany]

I have had excellent results with a 40 tooth Forrest WWII blade with their "No. 1 grind" which is a true flat top grind. Cuts super clean. Down side is it is a relatively expensive blade. Leaves a perfectly flat bottom as seen on this Doug Stowe inspired jewelry box.
IMG_0475.jpg

[Edwin Santos]

Why not just use a good quality, full kerf ripping blade? You may have to get it resharpened to be exactly 0.125" width, but that doesn't cost much. This Freud is really close at 0.126" kerf: http://www.freudtools.com/index.php/...oduct/LM72M010 You need a backer board to prevent tearout so as long as the blade you choose cuts smoothly it should work fine.

John

I just ordered this same blade for a similar purpose as well as for cutting clean shoulders on dovetail joint tail boards (recent FWW article talks about this technique). There is a seller on Ebay selling this blade at a very low price, under $40 new. Like John notes, the kerf is .126. Not sure if .001 makes a difference for you. From what I know about the incremental screw drive jigs, it shouldn't.

[Kevin Groenke]

We have had good luck with this blade for box joints. A backer board eliminates tearout that you will otherwise probably get with any FTG blade.

https://www.amazon.com/Kempston-9931...dp/B0013KTUQ6/

[Wayne Jolly]

+1 on the Forrest Custom #1. I bought one at a woodworking show a few years ago ad it is one sweet blade. Very clean cuts with perfectly flat bottom kerfs.


Wayne

[Raymond Seward]

+1 on the Forrest Custom #1. I bought one at a woodworking show a few years ago ad it is one sweet blade. Very clean cuts with perfectly flat bottom kerfs.


Wayne

+2 I use mine a lot. It is price but top notch....actually I have switched to all Forrest blades...I've tried them all but now stick with Forrest

[Alan Schaffter]

Just remember, with an incremental box joint jig, the blade width/kerf created must be a perfect, whole number multiple of the pitch of the leadscrew (typically, a multiple of 1/32" or 1/16" for standard hardware store all-thread.) The tolerance is pretty tight, too, just a couple of thou. If it is off by as little as .003" you won't get a good joint. Also, the all-thread and follower (nut) must fit together well, it is best if they have close tolerance threads, to limit backlash (engineering). Compensating with fractional revolutions of the crank can be a real nightmare to track.

As an unabashed self-promotion- the INCRA I-BOX doesn't have this problem- you set it to the width of the blade kerf, whatever it is (the jig doesn't care), by direct transfer (no calipers or measuring of any kind).

[Benjimin Young]

An update to my quest for a 1/8” kerf FTG finish blade that will work with my newly built 1/16" incremental jig.
First off, thanks to all for the great responses, some great advice there. Here is what I have tried so far and the results. Hopefully, other can learn from my fun.

I have a few different Freud blades but did not have a 1/8” kerf FTG. So when I built the jig I tried the 1/8 kerf ATM Freud blade and got tight joints but as expected bottoms are not clean.,
I concluded that a 1/8 kerf would work but needed to find a FTG, hence this thread.
I took all the great advise and set out to find one but options were limited so I waited for the wood working show.
At the Hamilton wood working show last weekend I spoke with the Freud rep and purchased a Freud LM72R010 FTG heavy duty rip 1/8 kerf 24T 20 hook. I also purchased the Freud SBOX8 two blade set that does 1/4 or 3/8, great price at $99 CND.

Back at my shop several tests with my new 1/8 kerf FTG Freud rip blade produced very disappointing results with very sloppy joints even with just 1/8” keys. Just for fun I checked the slop with a feeler gauge, .011 slop with .012 to .013 just getting tight.

I now suspected my saw so I did a complete check of alignment - vertically over 360 degrees the blade is bang on, over the length of the blade at full height the blade has .003 runout in relation to the table slots.

Then I remembered the first test I did so I repeated it (the Freud 1/8 ATM plywood blade) and it resulted in tight joints again albeit with bad bottoms

Next I setup the new SBOX8 Freud box joint set at 1/4" and got great tight joints.

Conclusion, I am now wondering if a FTG blade designed for ripping is never made to kerf spec tolerance suitable for my purpose, in which case it is luck of the purchase.
Or, is the LM72R010 blade I purchase not made to Freud spec, aka defective ?. I will ask the vendor if I can return it.

So, I will continue to use the Freud BOX joint blade set, very nice, and do box joint 1/4" or larger keys. If I want to do 1/8 keys I may try again for a different 1/8 kerf blade but only if I can return the one I bought at the wood show (budget blown for now ;-).
Happy woodcuttingJ