MFT - Why?

[petermillard]

@petermillard what I find useful is that you are not restrained by any angle and they come in handy for not only workbench tops in conjunction with dogs but also for making a high fence for the mitre saw or router table or there are many jigs that can be knocked up, just a piece of MDF and some slots and you have a jig for a given purpose. It is so easy to run the slots that I now make most jigs adjustable rather than a fixed setup for a specific task.

Yes, indeed; but are they any better than eg a routed t-slot?

 

[johna.clements]

But don't they have a fixing underneath which can be a problem with access.

They just hook under the MDF. As long as you have about 40mm ish clear vertically under the table you can insert down through the dog hole then turn to the horizontal. Then you need enough horizontal clearance under the MFT the direction you want the clamp to operate. So if you were to support the MDF those camps could only be used pointing away or parallel to the support.

Added

I am talking about the guide rail type clamps where they are small enough. If they are too big they will not be able to turn in a 20mm dia 18mm thick material.

 

[Spectric]

Yes, indeed; but are they any better than eg a routed t-slot?

good question, an even better one for microjig! Maybe it is in the profile, with a T slot you have corners and we know things fracture at corners wheras a dovetail has no corners as such plus the upward force has more area to resist, the T slot only has the material left above the lower slot. Someone needs to make a video comparison .

 

[johna.clements]

good question, an even better one for microjig! Maybe it is in the profile, with a T slot you have corners and we know things fracture at corners wheras a dovetail has no corners as such plus the upward force has more area to resist, the T slot only has the material left above the lower slot. Someone needs to make a video comparison .

Last time I looked dovetails have corners in them!.

I doubt that aluminum t track would fail at the corners, maybe 80N/mm2 in tension and 50N/mm2 plus in shear depending on grade. Ply has a shear strength up to about 8N/mm2. Wood glue is about 2N/mm2.

A clamp with 60mm running in a routed slot will be trying to shear off the ply, mdf etc on the sides of the slot.
A clamp in T track will be trying to pull out the fixings plus any glue.

A routed slot on a thin sheet is likely to be stronger than very short screws. A t track screwed or bolted down to a thicker sheet will very likely be stronger.

 

[Spectric]

Last time I looked dovetails have corners in them!.

But not 90°, aluminium T track may not fail but a T slot routed into MDF has to be weaker because there is less material remaining to resist the pulling force compared to a dovetail.

 

[bertterbo]

But don't they have a fixing underneath which can be a problem with access.

I very rarely use the locking screw.

 

[Jake]

Do you mean the plastic parts or the thin edges of the wooden dovetail itself?

If it's the latter, it reallys quite adequate. If you think about it, the timber isn't really under any kind of stress on it's thin components. It's only really compression. So unless your plywood has voids in it, it works perfectly fine.

Both. Plus what must be all the pfaff with detritus in the channels - I'm too messy.

 

[johna.clements]

But not 90°, aluminium T track may not fail but a T slot routed into MDF has to be weaker because there is less material remaining to resist the pulling force compared to a dovetail.

A routed dovetail to fit a clamp will be the same profile as a routed dovetail to fit a track in which a clamp is fitted. the dovetail track will have more material above it resisting pull out since it is slightly bigger because you have to allow for the wall thickness of the dovetail track. The dovetail track will also act like a continuous beam and spread the load along the length of the track, how far depending how stiff the track is. A dovetail with no track will only spread the load over the length of the clamp so will fail sooner.

 

[TRITON]

One of the issues with T track is that it is easy to pull it out of it's slot unless the board is thick enough so that you can use threaded fasteners rather than woodscrews. I have been using the microjig slots for over a year and with no issues, the system is just so easy to knock up fences and work supports as well as those odd jigs to get you out of a tight spot.

I'm guessing that youre speaking hypothetically and you've never actually had this happen. Seems like an argument to nowhere.

 

[Spectric]

I have had a T rack pull out of its channel, what you must ensure is the channel is flush with the surface otherwise the pulling force will make it flush against your workpiece, ie take up the clearance. There is a similar issue with dovetail slots, you have to pull against the workpiece otherwise you will pull the clamp out of the dovetail slot.

 

[johna.clements]

I have had a T rack pull out of its channel, what you must ensure is the channel is flush with the surface otherwise the pulling force will make it flush against your workpiece, ie take up the clearance. There is a similar issue with dovetail slots, you have to pull against the workpiece otherwise you will pull the clamp out of the dovetail slot.

Dovetail slots with no track have the advantage where as you note you can arrange your work so you can clamp against it. They are also cheaper and can be installed quickly.

If the work piece is not above the track or dovetail and the fasteners have sufficient capacity (as you note maybe threaded fasteners) then square or rectangular track would have a higher holding capacity rather than just a clamping capacity.

 

[TRITON]

T track is held in with multiple fasteners, plus the material itself is rigid. For something to simply pull out, it would take considerable force to do so to overcome all the fasteners.

Obviously this type of tthing is not a new idea(It just occurred to me at the time) to combine T track and bench dog holes and can be seen here on the UJK site.

Many companies do hold downs that run in T track, so I wonder what level of force would be needed to pull the track out its slot, overcoming the fasteners Certainly not enough from a simple hold down. You would need considerably more than that, and then given its rigidity and its multiple fixing points i wonder what would give first, given the pull force you must be be talking about, what would give first, the track itself or whether the T slot bolt would rip through the thin edges of the alloy..

I wonder is in this seemingly hypothetical reasoning, if posters are taking into account the use for T track in an MFT type bench. where the use of the track is to accommodate workstops, to hold the guide rail or component at different angles, and not as some sort of clamping area to put hundreds of kg of downward force as in a glue up type scenario as was the type of thing myself and Deema were referring to it for.

 

[Distinterior]

I wonder is in this seemingly hypothetical reasoning, if posters are taking into account the use for T track in an MFT type bench. where the use of the track is to accommodate workstops, to hold the guide rail or component at different angles, and not as some sort of clamping area to put hundreds of kg of downward force as in a glue up type scenario as was the type of thing myself and Deema were referring to it for.

I was wondering the same thing...!!
If I was of a mind to want to excert that kind of pressure or force on T track, I'm sure i would find a stronger, better way of holding the workpiece.
The MFT / T track scenario does work well on small components, sheet materials etc, but if I wanted to hand plane a large section of material, I would likely find a better way of holding the timber.

 

[johna.clements]

T track is held in with multiple fasteners, plus the material itself is rigid. For something to simply pull out, it would take considerable force to do so to overcome all the fasteners.

Obviously this type of tthing is not a new idea(It just occurred to me at the time) to combine T track and bench dog holes and can be seen here on the UJK site.


Many companies do hold downs that run in T track, so I wonder what level of force would be needed to pull the track out its slot, overcoming the fasteners Certainly not enough from a simple hold down. You would need considerably more than that, and then given its rigidity and its multiple fixing points i wonder what would give first, given the pull force you must be be talking about, what would give first, the track itself or whether the T slot bolt would rip through the thin edges of the alloy..

I wonder is in this seemingly hypothetical reasoning, if posters are taking into account the use for T track in an MFT type bench. where the use of the track is to accommodate workstops, to hold the guide rail or component at different angles, and not as some sort of clamping area to put hundreds of kg of downward force as in a glue up type scenario as was the type of thing myself and Deema were referring to it for.

The t track will act structurally as a continuous beam. But it is not very rigid so only a few screws either side of the clamp will be fully engaged because the track will deflect. If a flat plate was attached on the under side of a MFT with set screws from the track to the plate to clamp the track and plate together you would likely get a a deeper beam which would be much stiffer. The track would then have much lower delflection and you would have to shear the MFT eitherside of the track to pull it out.

 

[bertterbo]

With T-Track. You really want to be using a clamp like this, as then you're not pulling the track out of the channel. The force is compressing the pieces, rather than pulling up on the track (same with the dovetail clamps)

 

[Sideways]

Utterly unconvinced of the T track argument.
The pitiful little screws that are all you can usually fit to hold it down without obstructing the track are totally inadequate to resist clamping forces and if you can't pull on them what's the point.

The original festool method of lever clamp poked through a hole is simple and strong.

If you do need to use T track for clamping, then spend a few quid on dovetail T track and make sure it's a good tight fit in the slot. This had to be hammered in.

Just my opinion ...

 

[bertterbo]

You can also use epoxy to hold it in. Which will be pretty strong.

In regard to the screws, I always use overly long ones, then grind the bit sticking out. This way you get more thread into for example 18mm ply.

 

[johna.clements]

Utterly unconvinced of the T track argument.
The pitiful little screws that are all you can usually fit to hold it down without obstructing the track are totally inadequate to resist clamping forces and if you can't pull on them what's the point.



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why not counter sink the channel so you can use longer screws or use a counter sunk set screw. Screwfix sell 3mm X 30mm screws. You can buy counter sunk M3 x 30mm machine screws, M4 x 50mm

 

[Spectric]

@Sideways has picked up on those little screws, if you use 22mm MDF then you will only have 12 or 14 mm in which to screw the fasteners and @bertterbo s drawing illustrates the issue with both the T track & dovetails if you dont apply the forces in the right direction and also note that T track comes in straight or tapered external profile but either way it can move. Solution is to fasten right through with penny washers and nuts on the back so then it cannot move or back it with enough wood so you can use longer screws. I will still say the dovetail slots are cheaper because the one cutter can produce as many slots as you want and they are so flexable but like anything need to be used in the right way.

 

[johna.clements]

@Sideways has picked up on those little screws, if you use 22mm MDF then you will only have 12 or 14 mm in which to screw the fasteners and @bertterbo s drawing illustrates the issue with both the T track & dovetails if you dont apply the forces in the right direction and also note that T track comes in straight or tapered external profile but either way it can move. Solution is to fasten right through with penny washers and nuts on the back so then it cannot move or back it with enough wood so you can use longer screws. I will still say the dovetail slots are cheaper because the one cutter can produce as many slots as you want and they are so flexable but like anything need to be used in the right way.

Thanks for confirming what I have stated.