Biscuit Jointing - how tight a fit for biscuits?

[TonyW]

I have recently been using a Ferm biscuit jointer to put together some frames. This is a machine I bought some years ago on impulse (it was only £30 ) and has not been used very much until recently.

I noticed that the biscuits just dropped into the slot requiring no help from me. On investigating a little further the biscuit sits in the slot with a gap of about 1/2mm (using mark 1 eyeball ). The original biscuits were No. 20 bought from Screwfix and I also have Trend No. 0 and No 10. purchased recently. I notice that the Trend biscuits slightly thinner than the Screwfix!

Now I know that the biscuit swells when moist with glue - I decided to test how much by wetting a biscuit and slot with plain H2O. A couple of hours later I could not get the biscuit out by hand. So I suppose it could be argued that its all working!

But I still have a question. How tightly should the biscuits fit prior to glueing - I would have thought that they should at least be a snug fit?

Cheers
Tony

 

[OPJ]

There's often some variation between the thickness of biscuits inside a single pack or box. If you find they're too tight, usually, giving them a few seconds in a microwave is enough to make them fit.

I don't think I've had any that slop about in the slot... I'd probably pre-soak them, as you have done.

 

[woodbloke]

Biscuits ought to be a push fit into the slot, .5mm play seems a bit excessive to me. I use Trend and Lamello biscuits which are both fine and I keep them in an old coffee jar with a few grains of rice in the bottom to absorb moisture - Rob

 

[TonyW]

Thanks for your replies - confirmed my thoughts that they should not move in the slot and ideally would need to be pushed home.

So it would appear it is either down to technique or poorly aligned/designed blade (still the original). I suspect the latter due to the fact that work was clamped to the bench and I used the base of the jointer on the bench rather than the fence.

I will have another play after checking blade is not wobbling. Perhaps I should invest in a new blade - just did a quick check and a new CMT blade costs as much as the original purchase price for the whole kit :shock:

Cheers
Tony

 

[Steve Maskery]

Just thought. When you used the word "wobble" it brought to mind wobble saws. If the blade is not simming true on its axis, it will, indeed, cut a slot that is too wide. I'm not sure how you would test for this though.

Cheers
Steve

 

[mailee]

I am sure this is the blade on the Ferm machine as I too have one with the same problem. I also have the cutter for the router and this is a perfect fit for the biscuits. I havent replaced the blade in my machine for the same reason as you it is expensive compared to the Ferm machine. I suppose I should bite the bullet and buy one really but I don't use it enough to warrant it. :roll:

 

[Derek Willis.]

I am sure that a new blade, and not very expensive at that, will cure your problem.
Derek.

 

[TonyW]

Thanks for the additional replies. I have now taken the unit apart to check the blade etc. Unfortunately I could not figure out anyway to check the blade for flatness as the teeth seem to be set slightly offset every alternative tooth. So I am assuming that this blade is ok - at least as good as it gets for this mnfctr.

I also found that the cutting depth was way off at around 18mm (should be 12.3mm) so this is now fixed The picture below shows the adjusted cutting depth at the top and below the incorrect depth slot.

This picture shows the biscuit fitted with a folded piece of paper approximately 0.50mm - this is a snug fit and requires a gentle push to locate the biscuit!

So, I am hoping that the fault is in the blade rather than the axis is out ! New blade on the cards then but which one - is there are cheaper alternative to the CMT @ £30?

Cheers
Tony

 

[BigShot]

I have a suggestion for checking the blade.

Lay it flat on as flat a surface (herein "bench") as you have and measure from a marked point on the bench to a point on the main disk (herein "disk") at a point between the teeth.

You should then be able to rotate the blade, keeping it as much in the same place as you can, and take more measurements from the same point on the bench and different points on the disk.

If the disk isn't flat, I'd expect the measurements to vary and to stay the same if it is.

It might work anyway.

 

[TonyW]

Thanks BigSHot liked your suggestion at first then after some consideration decided against it - purely on me being able to take accurate measurement down to 0.25mm.

This is based on my understanding that the kerf should be around 4.0mm for a snug fitting biscuit. My testing revealed a kerf of around 4.5mm with my blade. I am assuming that the offset of the teeth are designed to clear the sawdust away from the blade. If this is the case then it would take only 0.25mm on either side to throw things out. So I talked myself out of this test :roll:

Decided to bite the bullet and ordered a CMT blade from Axminster hoping that this will resolve the issue.

Cheers
Tony

 

[TonyW]

After having a further play and a thorough check I think I may have found the problem - the base plate would not close perfectly as shown below (exaggerated pic). Due to the dust collector connecter.

Removing the dust collector allowed the base plate to close correctly

Trial cuts without dust collector allowed biscuits to sit perfectly in the cut!

So the indication is that the connector is just a little too large and also I believe not truly circular. I am about to take some sandpaper to the connector to try and rectify this.

Well I needed a new/spare blade anyway.

Cheers
Tony

 

[chippy1970]

I dont like those Screwfix biscuits they are a bit rough and furry, the ones I got were anyway not neat like the Trend or Lamello ones.

 

[MickCheese]

I had some problems with my Wickes jointer.

I found that the blade in that had a 3.5mm kerf while the biscuits were definitely wider. I bought a Fraud blade with a 4mm kerf and no more problems.

Mick

 

[TonyW]

Shame I did not know about that before could have bought a Wickes replacement blade and with my offset of .50 would have been perfect 4mm :lol:

 

[ivan]

Lamello biscuits are a "nominal" 4mm to fit an accurate 4mm slot cut by a 100x4x22mm blade. A 3,5mm biscuit jointer is not fit for purpose unless sold as part of a special Wickes 3,5mm biscuit system. Apart from special mini biscuits, I've never seen any biscuits that were not supposed to be to Lamello sizing. Manufacturing errors might cause a blade to wobble-cut and so make a wider groove; maybe Wickes were relying on this!

Wobbly bicuit joints at assembly can somtimes cause alignment problems, in which case a dowel might be helpful, but usually they swell up so xxxy fast you have to use a deadblow mallet to knock things into place!

 

[TonyW]

Just a final update. Have now just fitted the CMT blade - quite a difference biscuits fit nice and snug - now not such a bad tool!

When I lay both blades on a flat surface there was a small amount of 'rock' on both sides of the Ferm blade - CMT had no 'rock'

Thanks for all your help

Cheers
Tony

 

[wrightclan]

Yeah, I used to have a Ferm Jointer with the same problem. I replaced the blade with a Freud Blade. Problem fixed.

Actually it wasn't a bad biscuit jointer (with the Freud Blade). It was quite accurate, if I worked from the base. The fence was a little less parallel to the blade, but still not bad for the money. I use the base as a reference point on at least 95% of cuts.

(I now have a Freud Biscuit Jointer.)