Biscuit Joints

[rcp612]

I'm confused as to if I'm doing something wrong or if everything is just as it's supposed to be.
I've seen "Nahm" using biscuits and during a dry fit, he tapped them in place with a mallet. When I do a dry fit all I need do is get them close and they fall in.
I checked the adjustment on my joiner (Freud JS100A), experimented with the adjustment, and tried various size biscuits. It seems as though the slot is alright lengthwise but, too wide for the biscuit. What is right???
As is, these are no support at all, just extra gluing surface. But, "Nahm" keeps saying that they help align the 2 pieces. Not in my experience with them.

[Rand]

I have a Dewalt biscuit cutter and with the Porter cable brand biscuits they are definitely loose. The biscuits are loose enough that I can adjust the boards while in the clamps and get things lined up. They help align the boards a little but you still need to tweak it.
My understanding is that the moisture in the glue swells the biscuit and makes for a tight joint. I've never had a biscuit joint fail in my projects.

[JR]

Sounds to me like you've got a problem. Possilbe causes:

1. Bad batch of biscuits, formed at improper thickness.
2. Bad cutter. This could be blade wobble or blade thickness.
3. Bad technique. If the biscuit joiner moves during the cutting process, you could very likely experience a slot that's too wide.

I'd favor attacking number 3 first. At least that's what I would suspect in my shop. FWIW - On a recent NYW program I saw Norm hold down the fence with his thumb, therefore keeping the tool aligned and motionless during cutting.

JR

[JimD]

I last bought biscuits several years ago - maybe 5-10 years ago. I store them in the bags they came in which don't seem well sealed to me. With that introduction, my Skil biscuit jointer slots are small enough I sometimes need a mallet to put them in and pliers to take them out. I think it is that my biscuits have swelled a little from humidity but I am not 100% sure. I buy 1000 at a time. Initially an assortment and later some more #20s.

Jim

[dbhost]

With my Ryobi JM82K Biscuit Joiner and PC biscuits, the biscuits slide in with some noticable friction.

Might be blade wobble?

Having to tap the biscuits in like you see Nahm do doesn't make sense to me...

[just started]

Mic your cutter head cutting edges and compare the largest to an adverage of a dozen #20 biscuits. If that is close enough to give a friction fit then check for runout or wobble of the cutter head and exactly square between the cutter and face. If that all checks out then look to user error.

[herb fellows]

I have the pc biscuit joiner, and I had a similar experience when I first used it, the biscuit seemed way too loose. So I cut a couple of slots in some pine and brought it to a show and talked to the PC guy there. He told me they were ok.
I haven't really tried to rip apart the pieces I've test fit, maybe I should be doing that.
Other than taking it apart, it seem as if there is no good way to see if the biscuit has swelled properly and is indeed helping the joint.

But I don't understand why Norm would be using a mallet; if they were that tight going in, and then they are supposed to swell, wouldn't this be causing some problems?

[messmaker]

I would suspect that your biscuits picked up a bit of moisture. Might try putting them in a very very very low temp oven for a while.

[cabinetman]

Sounds to me like you've got a problem. Possilbe causes:

1. Bad batch of biscuits, formed at improper thickness.
2. Bad cutter. This could be blade wobble or blade thickness.
3. Bad technique. If the biscuit joiner moves during the cutting process, you could very likely experience a slot that's too wide.

I'd favor attacking number 3 first. At least that's what I would suspect in my shop. FWIW - On a recent NYW program I saw Norm hold down the fence with his thumb, therefore keeping the tool aligned and motionless during cutting.

JR

JR's solutions would be a good starting place. I'm not a big fan of biscuits and use them only as a last resort and don't rely on them for alignment. The spacing problem explains that. Here in South Florida, the humidity can go from 50% to 95% in the same day. I get a wide variance of biscuit thicknesses. For how inferior they are, I would rather use a wood spline.

Tapping in the biscuits could damage the edge.
.

[LCHIEN]

my experience:
i have to tap them in, sometimes use pliers to remove them (dry)
I have a dewalt BJ.

if yours are loose, as long as they don't "rattle" you may be OK.
if they rattle around that's not good, if they go in easily you want at least a "slip fit". The water content of the glue will swell them to fit the slots sugly when you do the final assembly.

To tighten up the fit, make sure you re holding the BJ steady and not moving up and down while cutting. I try and hold the fence flat on top of the workpiece while I plunge the cutter. so thatthe cutter goes straight in and out.

Maybe moistening the biscuits slightly will cause them to swell (as the glue will do).

[Salty]

I just did some banding on 3 sides of some plwood to make cabinet tops. The banding is 3/4 x 1.5" and the plywood is the 'less than 3/4" stuff' that is imported.
I noticed that the finished edges didn't always end up flush. I think it is a combination of my laziness and a cheap skil jointer. I didn't want to reset the fence for the thinner plywood so I mistakenly thought that if I just reference the finish side down on both pieces and keep the jointer pressed down on the table then it should be correct. I think the jointer vibrates too much and still moves enough to slightly change the width of the slot and the location. Some of the biscuits fit tight and some loose.
Also, I was too concerned with pressing down on the jointer and may not have held the thinner plywood tight enough to the table. Although now that I think about it, the plywood was too high in the problem areas so that would mean the jointer would have had to have moved up away from the table. I was always sure to clean away the sawdust before each cut. Maybe the blade is wobbling...I'll have to check.
I also get in too big of a hurry and don't clamp everything down to the table like I should.
Yea, sometimes I'm lazy.

[drumpriest]

Great discussion! My PC cuts them a bit loose as well, part of why I'm not much of a fan. I would say that it isn't technique, as my domino cuts are very tight, and it requires a better touch, if you get my meaning. I don't know if it's the biscuits or the cutter. I pretty much don't use biscuits anymore though, might even sell the joiner...

[RayintheUK]

I've seen "Nahm" using biscuits and during a dry fit, he tapped them in place with a mallet. When I do a dry fit all I need do is get them close and they fall in.

Firstly, as far as I recall, every time I've seen Norm use biscuits, they've always been right there on the bench, never randomly selected from a container. It might be my overly-cynical view on things, but I don't think that's a co-incidence! If he was trying to demonstrate the advantages of lining up the faces of pieces to be joined, he'd hardly use ill-fitting or floppy biscuits, would he? Given the amount of pre-recording tinker-time available, I'd try to get everything perfect too, so I don't blame him or his team for that.

Another factor to consider is the source of your biscuits. Are they a "no-name" make, or a reputable brand name? I've tried any number of alternatives over the years, but I've realized that - yet again - you get what you pay for. I get mine from the manufacturer of my biscuit jointer and I've never had a problem since.

I checked the adjustment on my joiner (Freud JS100A), experimented with the adjustment, and tried various size biscuits. It seems as though the slot is alright lengthwise but, too wide for the biscuit. What is right???

As you'll know, the depth of the slot (and - therefore - the horizontal width of it) is controlled by the plunge depth of a fixed (100mm) arc. In order to get the biscuits to fit correctly far enough into the wood, there will always be some side play (due to the shape of the biscuits) - which can be an advantage when lining up panels laterally, prior to clamping.

The vertical width of the slot, however, is controlled by the kerf of the cutter - which should be 4mm for standard biscuit sizes ("0" "10" and "20"). However, this can vary, as JR points out earlier in the thread - either by cutter run-out, or variations introduced by operating technique.

As is, these are no support at all, just extra gluing surface. But, "Nahm" keeps saying that they help align the 2 pieces. Not in my experience with them.

If you're plunging off the same section of a datum surface (the workbench) with the face of the workpiece downwards, then the slots should line up perfectly. If, however, in spite of this technique, the slots are still wide enough to allow vertical movement, that would reveal an unacceptable amount of cutter run-out or wobble - the cutter kerf itself is so unlikely to be at fault, you can discount it - or unacceptably-sized biscuits.

I wrote a page a while ago which contains more on technique, etc. here, which may help if you get the time.

Ray.

[cabinetman]

Firstly, as far as I recall, every time I've seen Norm use biscuits, they've always been right there on the bench, never randomly selected from a container. It might be my overly-cynical view on things, but I don't think that's a co-incidence! If he was trying to demonstrate the advantages of lining up the faces of pieces to be joined, he'd hardly use ill-fitting or floppy biscuits, would he? Given the amount of pre-recording tinker-time available, I'd try to get everything perfect too, so I don't blame him or his team for that.

Ray.

That's an understatement, and so true. We watch these programs and have no idea how many takes it took for a no "flub up". We also don't know how many "experts" consulted with the "actors" to enable them to put on a good show. And as for the products and tools, I agree, they all are likely "hand picked". I can't remember a show where the demonstrator picked up a tool and it died on the spot. Maybe if it did, that segment would be "take #19" or whatever number it takes.
.

[rnelson0]

I've seen "Nahm" using biscuits and during a dry fit, he tapped them in place with a mallet. When I do a dry fit all I need do is get them close and they fall in.

On a dry fit, I am always able to slide biscuits in with no problem (exception: sometimes a biscuit has a splinter sticking off to the side). When I add glue, however, usually I have to push the biscuit in. I do not know that a mallet is needed, and it may spray glue everywhere anyway I would really worry about how tight the fit is with glue. Give it a shot on some scrap and see if it is snug with glue.