Tweaks on cutting with round dogs/MFT

[rmwarren]

After using my MFT and TS55 for about a year now I have really have come to value what they are capable of in terms of clean, accurate cuts. With that said I have never really liked the implementation of the hardware for the rail guide and angle unit. They work beautifully, but I find them cumbersome and often in the way, with the angle unit sticking off of the table and the rail upright and prone to dropping on my head. I also seem to snag my shirt or apron on the front bracket on a daily basis.

If I am using the table for non-cutting activity (w/o the guide and rail attached) and then need to make just a couple cuts I often freehand them instead of taking the time to reattach the guide and rail.  I was really looking for a simpler way to make a few cuts while still maintaining precision and repeatability for my most common 90 and 45 degree cuts.

I have also been using the round dogs a lot and really appreciated their utility and precision. After spending a fair amount of time staring at the MFT (often with a cigar and beverage in hand) I came up with an idea that I have been having some success with.

The primary idea harnesses the precision MFT holes grid with the dogs (nothing new, credit to Qwas and others) but tweaks the concept to fix in place the guide rail while simultaneously height-adjusting it. This is similar in practice to Qwas’ rail dogs, but uses a modified dog bored out to accept a pin, clips that attach to the rail, and one or 2 more dogs to align the material at 90 or 45. The modified dogs/pins are used to reference the edge of the guide rail while the angled clips lock the rail in snug to the pins and prevent it from moving. The rail just slips into place along the pins and locks itself securely. Everything drops into my apron pocket when not in use.

This is the setup for a 90 on narrow stock, 2 dogs with pins and one more dog to align the stock:

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This is the modified dog:

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This is the angled rail clip:

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The rail engaged with the pin:

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Setup to cut a 45 on narrow stock:

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Rail engaged with pins for a 45:

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Maximum capacity lengthwise on the MFT is just less than 37” (using the 55" rail), on the narrow axis it is 21-3/4”.

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Using 2 dogs to align the stock and 2 for the rail, the dog with the pin does double-duty:

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The 2 minor negatives I have noticed are the need to support the near end of the rail with a scrap of the same thickness that I am cutting, and the width of the rail causes the cut in the MFT top to end up running over another set of holes.

Again, the basic concept is nothing new; it’s just a twist on the utility of the original precision dogs supplied by Qwas and others. I don’t think this will totally replace the MFT components, but for me it works great for common 90 and 45 cuts and takes seconds to set up.

These components are all rough prototypes I am tweaking, I am considering making up multiple sets, all CNC 6061 aluminum, and offering them for sale if there is any interest. the next iteration will use a low-profile dog (head height of about 5mm) and I will be able to cut ¼” plywood and up.

Comments or improvements are welcome.

RMW

 

[Alan m]

thats a great idea. i have rail dogs but dont use them that much because of the way they bind in the holes tring to set the piece under the rail.
i like the way the rail can be removed but still be able to set up the cut and then drop the rails on and go

 

[jmbfestool]

Nice idea!  I like it!   So der is no play in that setup then at all?   It looks like it could move with them pins sticking up like that by a mm or less.

JMB

 

[rmwarren]

Nice idea!  I like it!   So der is no play in that setup then at all?   It looks like it could move with them pins sticking up like that by a mm or less.

JMB

Thanks JMB.

I bored these dogs out on a small metal lathe and overshot the hole size by a few thousands of an inch so there is a tiny bit of slop (I am not much of a machinist), but in my test cuts it did not transfer to the wood. There will be no play in the next sets I do, they will be CNC machined. The pins are hardened steel, precision dowel pins and are accurate to +/- .002" so as long as the holes are bored for a precise slip fit there should be zero slop.

RMW

 

[JeromeM]

These components are all rough prototypes I am tweaking, I am considering making up multiple sets, all CNC 6061 aluminum, and offering them for sale if there is any interest. the next iteration will use a low-profile dog (head height of about 5mm) and I will be able to cut ¼” plywood and up.

I am interested.
Why not have all dogs able to use the rail projection? This would simplify usage and avoid having to keep some for only that use.

Another thought is that as you already have a hole in the other dogs why not have a matching pin in the rail projection? Again avoiding having to have a second type of base dog.

I don't know if either of these ideas make sense but they would simplify things

 

[andy5405]

I think your idea is brilliant especially as the rail can still be used in other ways without having to remove the dogs.  I wondered whether or not you need to use the separate pins at all. Why not just make a dedicated pair of rail dogs out of a single piece of aluminium. It would improve on accuracy. They could still be used in other places and would only get in the way if you wanted to pass a sander etc over the edge of a workpiece.

Have you considered slightly increasing the diameter of the base of the dogs. My thoughts are that there would be a significant bending moment exerted by the rail on the dogs especially if you were to cut thicker material. Would a slightly wider base seated on more of the table reduce this.

Also on the same subject do the dogs have to be a really tight fit in the holes to reduce the lateral movement at the top of the dogs? If that is the case, would that pose problems with the variance in hole sizes between newer and older MFT's and homemade tops made with a 20mm bit.

You mentioned that the blade cuts through a line of holes. Could you offset this by making the brackets on the rail slightly wider. It wouldn't affect accuracy and they would hardly be in the way or cumbersome even if they stuck out of the side of the rail by another inch more.

All in all I love the idea. I am working on something similar and have spent hours trying to devise a quick and simple way of securing the rail to the dogs. Everything I came up was way too complicated and impractical. Your idea is simple and effective.

 

[rmwarren]

These components are all rough prototypes I am tweaking, I am considering making up multiple sets, all CNC 6061 aluminum, and offering them for sale if there is any interest. the next iteration will use a low-profile dog (head height of about 5mm) and I will be able to cut ¼” plywood and up.

I am interested.
Why not have all dogs able to use the rail projection? This would simplify usage and avoid having to keep some for only that use.

If you are suggesting that all four dogs be bored out to accept the same pin I think I agree. I don't really see a downside to this.

Another thought is that as you already have a hole in the other dogs why not have a matching pin in the rail projection? Again avoiding having to have a second type of base dog.

I am not sure I totally understand, are you suggesting the pin be affixed to the rail clip rather than sitting in the bored out dog? I had not considered this but it has merit. I had to balance the length of the pin to allow the rail to raise high enough to cut 1-3/4" material while still being low enough that the saw's motor housing did not hit it. If the pin is too low it won't engage the clip with thicker material, if it is too high the saw hits it on thin material. The current pin height is right at 2-1/4" above the table.  On 1/2" material the saw just clears it; I have not tried anything thinner.

If the pins were fixed to the rail clip and slipped up and down inside the dog hole this issue would be eliminated, but they would hang below the rail and have to be removed to use the rail for other purposes. This is something to consider, I think there are pluses and minuses either way.

I don't know if either of these ideas make sense but they would simplify things

Great feedback,  these are ideas I have not considered. Thanks for the input, keep it coming.

RMW

 

[rmwarren]

I think your idea is brilliant especially as the rail can still be used in other ways without having to remove the dogs.  I wondered whether or not you need to use the separate pins at all. Why not just make a dedicated pair of rail dogs out of a single piece of aluminium. It would improve on accuracy. They could still be used in other places and would only get in the way if you wanted to pass a sander etc over the edge of a workpiece.

Have you considered slightly increasing the diameter of the base of the dogs. My thoughts are that there would be a significant bending moment exerted by the rail on the dogs especially if you were to cut thicker material. Would a slightly wider base seated on more of the table reduce this.

Also on the same subject do the dogs have to be a really tight fit in the holes to reduce the lateral movement at the top of the dogs? If that is the case, would that pose problems with the variance in hole sizes between newer and older MFT's and homemade tops made with a 20mm bit.

You mentioned that the blade cuts through a line of holes. Could you offset this by making the brackets on the rail slightly wider. It wouldn't affect accuracy and they would hardly be in the way or cumbersome even if they stuck out of the side of the rail by another inch more.

All in all I love the idea. I am working on something similar and have spent hours trying to devise a quick and simple way of securing the rail to the dogs. Everything I came up was way too complicated and impractical. Your idea is simple and effective.

Andy,

The reason for the bored dogs was to reduce the number of different parts I need to have machined. I was planning to make all the dogs with the .5" bore, if I do a dog w/ integral pin and a dog w/o pin I have 2 different parts and lose some benefit of quantity pricing. The pins, on the other hand, are stock items I can buy in whatever quantity I need.

RE: Deflection I have not looked too closely at this yet, my overall impression from test-cutting 1/2" and 3/4" material was that this was a minor concern but I have to do some more testing with an indicator to measure it. Your idea of a larger flange on the dogs has merit. I believe that deflection is minimized by the non-slip strip on the bottom of the rail and because the pressure exerted in the cut aligns with the cut direction rather than side-to-side, but this warrants a lot more testing.

I don't have a solution for odd-sized holes, I was aiming for the most common 19.9MM hole. If I am going to produce these in a cost-effective quantity the up front capital required is several thousand dollars, I can't justify the added cost to accommodate non-standard hole sizes.

I like the idea of extending the clips to move the rail past the holes. I kept the rail slightly proud of the clip to make sure the pin actually referenced on the rail and not the clip, the idea was not to introduce any error from the clip itself. If I extend the clip past the rail it just has to be designed to assure that it self-aligns to the rail and both clips add the same extension to each end of the rail. This is not hard to do, and probably is not a big concern, if they are out a few thousands over a 20" + spacing it shouldn't show up in material being cut.

Thanks for the input and ideas.

RMW

 

[JeromeM]

Another thought is that as you already have a hole in the other dogs why not have a matching pin in the rail projection? Again avoiding having to have a second type of base dog.

I am not sure I totally understand, are you suggesting the pin be affixed to the rail clip rather than sitting in the bored out dog? I had not considered this but it has merit. I had to balance the length of the pin to allow the rail to raise high enough to cut 1-3/4" material while still being low enough that the saw's motor housing did not hit it. If the pin is too low it won't engage the clip with thicker material, if it is too high the saw hits it on thin material. The current pin height is right at 2-1/4" above the table.  On 1/2" material the saw just clears it; I have not tried anything thinner.

If the pins were fixed to the rail clip and slipped up and down inside the dog hole this issue would be eliminated, but they would hang below the rail and have to be removed to use the rail for other purposes. This is something to consider, I think there are pluses and minuses either way.

I don't know if either of these ideas make sense but they would simplify things

Great feedback,  these are ideas I have not considered. Thanks for the input, keep it coming.

RMW

I clearly didn't make myself clear. All the dogs have a small hole in the centre. I guess about 6mm. So if you were to drill a corresponding hole in the extension (the one used to align the rail clip) and put a 6mm steel dowel in that then it would fit all the dogs. I would guess that it would be a cheaper option than counter boring the dowels. As an alternative getting stepped pins made would probably be less expensive than counterboring.

There is one possible advantage to having the pins drilled with a (6mm maybe) hole all the way through and that would be that they could then be stacked. What I mean is that as set would be at least 4 dogs 2 pairs of pins and 2 rail clips. The pins being sized to clear the saw motor on 12mm material (1/2") then the 2nd pair could be fitted to the first for significantly thicker stock. It may also be an idea to have the pins as pairs of different length's thus giving 3 different hights above table.

If this is not clear I will get to work in Sketchup to model the idea.

 

[rmwarren]

Had a little time to make the next round of prototypes for the guide rail clips, the latest are 1/4" aluminum and the rail is now offset 20mm, which prevents the saw from cutting across a line of holes in the MFT (thanks Andy).

I used them to cut a couple sheets of 3/4" ply for cabinets, so far no issues with alignment or accuracy.

No time to further tweak the dogs/pins yet.

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[rmwarren]

Another thought is that as you already have a hole in the other dogs why not have a matching pin in the rail projection? Again avoiding having to have a second type of base dog.

I am not sure I totally understand, are you suggesting the pin be affixed to the rail clip rather than sitting in the bored out dog? I had not considered this but it has merit. I had to balance the length of the pin to allow the rail to raise high enough to cut 1-3/4" material while still being low enough that the saw's motor housing did not hit it. If the pin is too low it won't engage the clip with thicker material, if it is too high the saw hits it on thin material. The current pin height is right at 2-1/4" above the table.  On 1/2" material the saw just clears it; I have not tried anything thinner.

If the pins were fixed to the rail clip and slipped up and down inside the dog hole this issue would be eliminated, but they would hang below the rail and have to be removed to use the rail for other purposes. This is something to consider, I think there are pluses and minuses either way.

I don't know if either of these ideas make sense but they would simplify things

Great feedback,  these are ideas I have not considered. Thanks for the input, keep it coming.

RMW

I clearly didn't make myself clear. All the dogs have a small hole in the centre. I guess about 6mm. So if you were to drill a corresponding hole in the extension (the one used to align the rail clip) and put a 6mm steel dowel in that then it would fit all the dogs. I would guess that it would be a cheaper option than counter boring the dowels. As an alternative getting stepped pins made would probably be less expensive than counterboring.

There is one possible advantage to having the pins drilled with a (6mm maybe) hole all the way through and that would be that they could then be stacked. What I mean is that as set would be at least 4 dogs 2 pairs of pins and 2 rail clips. The pins being sized to clear the saw motor on 12mm material (1/2") then the 2nd pair could be fitted to the first for significantly thicker stock. It may also be an idea to have the pins as pairs of different length's thus giving 3 different hights above table.

If this is not clear I will get to work in Sketchup to model the idea.

Yep- that clarified things. Actually there is no additional cost per se to counter-bore the dog, as long as it is machined that way to start with. The ones I used for the prototype were standard dogs so I did have that extra step but I can avoid it when doing a quantity run. The hardened steel pins are an off-the-shelf item which makes them cheaper than having to custom machine them.

My current concept is to have all 4 dogs counter-bored and just have 2 different lengths of pin to overcome any height issues.

Thanks for the input.

RMW

 

[rmwarren]

Update: It looks like I am getting enough interest to go ahead and make these, I kinda' hijacked another thread so there are more specifics now at:

http://festoolownersgroup.com/festool-jigs-tool-enhancements/festool-track-saw-and-parallel-guide-for-cabinet-construction-video/

RMW

 

[rmwarren]

I created a new thread consolidating the bench dog related stuff at:

http://festoolownersgroup.com/festool-jigs-tool-enhancements/mft-dogs-with-fs-cutting-guides/msg181502/#msg181502

Thanks,

RMW