CUTTING ON THE MFT - HELP NEEDED

[arso_bg]

Finishing the setup of my new customized MFT table I discovered that my saw instead of a straight cut makes a slightly curved cut (like a bow).

1. The table top is perfectly flat!
2. I checked the guide rail ? it seems OK
3. My saw is perfectly adjusted on the guide rail ? there is no side play.
4. When I make the cut,  the guide rail lies perfectly on the top of the material

What could be the reason for that? Any ideas? Did someone have such a problem?

 

[maxtool]

It looks like you're cutting MDF. If so, it's probably flat - but be sure.
It could be your guide rail. You may want to just give festool a call and ask for help.
I'd be interested to know the response. I've been having similar problems - but not the same - my cuts are consistently more toward the left side of the table at the end of the cuts.

 

[Notorious T.O.D.]

I just recently got my MFT3 and TS55 so I have hardly any experience cutting with it but one thing I noticed is that my guide rail when fastened at the rear of the MFT3 needs to be tugged slightly to the left at the front edge to fully catch the tab that locks into the bottom of the rail.  All appears to be square with the table and guiderail setup but I could see this possibly putting a very slight bow in the rail at the front and rear where they are attached but not pulling back the center where it is not attached.  I am not sure I am convinced that such a wide extrusion would have any tendency to bend in that manner over a littl more than 2 feet of length.  I guess the question I have is should I have to move the near end of the fence to the left to engage the slot with the tab sticking up or should it just line up much closer?  I think I could probably adjust it more if needed.

I guess in your case you could just try laying the rail over the two pieces and clamping the rail from under the table and see if you are still getting a curved cut.

Best,
Todd

 

[alanz]

If you have to tug the rail to get it to align with the tab, then it's slightly out of adjustment.

The procedure for adjusting the rail to the tab is in the MFT user guide, and it's as simple as loosening the two bolts at the hinge end of the rail, aligning the rail then retightening the bolts.

Mine was out of alignment for a while, and after the simple adjustment, now it's dead on.

 

[tbellemare]

Is your saw up to full speed at all times when it engages the material?

By that, I mean do you:

• start it;
• let it get to full speed;
• plunge it;
• cut;
• unplunge it;
• stop it?

I ask because the centrifugal force can change the shape of a blade somewhat.

Tom

 

[Dave Ronyak]

Arso_bg

I'm curious to learn what is the cause of your curved cuts, too.  I've never experienced anything like it.  Among the first cuts I ever made were full length bevel cuts to trim some new passage doors.

I have the older model MFTs and several other Guide Rails that I used with my TS 55 for ~3 years.

If you have another Guide Rail, try it in place of the one with which you are getting curved cuts.  I doubt it is the Guide Rail, though.  Also, try abutting the back edge of your suspect Guide Rail with a known reference straight edge (which could be a precision level or another Guide Rail) to see if there, indeed, is any curvature of the suspect Guide Rail.

I adjusted the stops on my MFT so the Guide Rail does not have to be tugged to the side, as recommended by one of Festool's factory representatives I have spoken with at several Festool demonstrations.  Other owners follow a slightly different teaching -- offsetting the stop nearest the operator so the Guide Rail has to be tugged a little toward the left to engage the tab.  What is important is that the Guide Rail fully engage the tab and be supported along its length and width so the Guide Rail cannot bow or twist during movement of the saw to make the cut.

Dave R.

 

[arso_bg]

Thank you all for your replies and happy New Year!

I?m afraid I didn?t describe the situation good enough. I am using a customized MFT table and the problem appeared after I have installed my new table top, during the procedure I use for squaring the fence to the guide rail. I cut two stacked pieces of 8 mm MDF than I flip the top piece. If the fence is square to the guide rail both pieces should align perfectly to the fence and to each other. As you can see on the pictures posted above, both pieces do not align to each other. 
The table top that I installed is made of a single piece 19 mm thick (?) MDF and measures 1865mm x 1165mm. Underneath the table top is supported by a wooden beam with levelers which is reinforced by an iron profile. (I wonder whether I should move the beam to support the table top exactly under the cutting line)

Otherwise I do everything according to the rules:

1. I checked the guide rail and it seems straight.
2. The guide rail is aligned well and I don?t have to pull it in order to align it with the tab.
3. When cutting I start the saw waiting to get it to full speed, plunge it, start the cut, finish the cut, unplunge it and stop it.
4. When cutting the guide rail lies perfectly on the top of the material

I don?t see an obvious reason for the result that I get.

 

[bill-e]

It seems to me that if the fence/rail are square the only reasons could be that either the work is moving or that the table is twisted.  Did you check the table with winding sticks?

 

[arso_bg]

Thank you for the advice Bill

The table top is flat. I check it with the Festool profile that you can see on the picture above.
But maybe there is still a slight movement of the table top downwards when I cut and apply a pressure to it. Maybe I need to support the top with a second beam or to move the existing one exactly under the cutting line. Now it is located in the middle of the table top.

 

[Notorious T.O.D.]

Arso,

One question, did your cut a known straight edge on the mdf to put against the fence prior to cutting the 90 degree crosscut?  I would because you can't count on the factory edge being straight for sure.  Just somethign else to consider in this puzzle.

Best,
Todd

 

[Forrest Anderson]

I think I'd take the rail off the MFT and try cutting a sheet of MDF with it on top of some sacrificial material on the ground. By eliminating the MFT from the equation, if you still got curved cuts, this would narrow down the problem to the saw and/or guiderail.

Forrest

 

[Dave Ronyak]

Arso,

I wholly agree with Forrest's suggestion.  I don't think a little deviation from true flat of your custom made MFT top is the source of your problem.  My Festool MFTs are not perfectly flat, and have no intermediate bottom side supports, and I do not have any problem making square crosscuts across panels.  Also, are the cuts curved or simply not a true 90 degrees?  The photos and description you first posted seemed to describe cuts that were curved or bowed.  Are you now getting different results?

Dave R.

 

[MarkF]

Are you sure the guide is absolutely flat on the piece of MDF?  I can have a gap when cutting thin stock near the fulcrum end of the guide d/t the height of the fence.  I also can have a slight uphill climb on the other end of the guide if I don't use a piece of scrap the same thickness as my workpiece to support the whole guide.  The slight flexing of the guide on either end could cause this slight error.  As suggested above...take the guide off the MFT, clamp it to your workpiece to eliminate shifting during the cut and see if it repeats.  If it does, burn the MDF because it's posessed ;D. 

 

[mastercabman]

Was the fence long enough so that the saw was sitting fully before entering and after exiting the pc. of MDF?
If you start your cut and the saw is only half way on the fence,the saw may not sit properly with the fence,causing off cut until the front and the back of the foot is fully engage with the fence.

 

[arso_bg]

Thank you all once again!

Yes Dave, you got the problem quite correct. It wouldn?t be a problem for me at all if the cuts were just out of square. I am having a problem with slightly curved or bowed cuts. And this is what makes me crazy.
On top of all ? this is the third table that I build and fourth table top that I change. All tables were made with the same profiles, used with the same saw and guide rails. Some of the tables were not perfectly flat but I had no problems with crosscutting of panels. Now I just changed the table top and added the supporting beam (what I consider to be an improvement) and run into this problem.
I also think that Forrest's suggestion is a very reasonable one. Thank you Forrest! Although I use my guide rails quite regularly and until now I didn?t notice any problems it is not a bad idea to check them all.

 

[Dave Ronyak]

Arso,

Please let us know the results of your further testing!  We'd all like to know what exactly is the cause of the "curved cut" problem you experienced and what finally solved that problem.

Dave R.

 

[Warrior]

Did you make sure the bevel knobs are tight?

 

[arso_bg]

Arso,

Please let us know the results of your further testing!  We'd all like to know what exactly is the cause of the "curved cut" problem you experienced and what finally solved that problem.

Dave R.

Of course I?ll let you all know about the solution. I am just not ready yet.

For the time being it seems that my guide rail has some deviation from the perfect straight line. It is that minimal that you hardly can notice it unless you cut two stacked pieces and flip the top piece (which doubles the mistake).

Unfortunately at the moment I cannot replace the guide rail on the MFT (and proof that this is the reason for the strange curved cuts) because this is the longest guide rail that I have. Since I already exceeded several times the reasonable budget that I can spend for my hobby it will probably take a couple of months before I get a new guide rail.

The most difficult question for me is how does it happen that until now I?ve got straight cuts with the same guide rail on the MFT? Here the only explanation that I have is that the table top that I recently replaced was far from perfect. It was build from two separate pieces of thinner (18 mm) MDF that were not supported in the middle. So the table top saged in the middle and obviously this imperfection compensated somehow the imperfection of the guide rail. At the end I had perfectly straight cuts!!
The new table top which is made of a single piece sturdier MDF, which is supported in the middle and perfectly flat does not hide anymore the imperfection of the guide rail. So the first cuts that I made on my new table top revealed this imperfection.

Regards

A.G.

 

[johnrichardson]

I think it may be that when you execute the cut the table is sagging very slightly , i would  have  joined two complete mft3  s together to get some firm" leggage" support at the point where you seem to have your cutting rail... the centre where the table is is weakest.  I would say that the alu extrusion they use is pretty rigid but over that span it will flex a bit ie sag so your cross  member underneath the  table will be only partially effective unless supported right to the floor maybe rig up a temp trestle there.  Another thing that could cause the table to twist laterally would be that as there are only four legs on your table the increased span will give an elevated leverage effect about the points above the  legs,  i would try and  brace  the  legs so there is no wobble there,

  my  mft 3 is a bit  wobbly at its normal  size  but i bet it  is a lot wobbblyier  when the top is extended double..  In conclusion  I would imagine its better to connect two  mfts to  get the  support under the  centre, more expensive  i grant you   but you can  dismantle it easier  for  versatility  or now youve got your long custom made which looks  elegant by the way... build some kind of supporting cabinet or trestle to eliminate sag/twisting effect on  those  4 overworked legs interesting to find out what the soln ws  johnr

 

[fshanno]

I don't know about the "flat" thing.  I don't think sagging would cause this.  When I cut on saw horses the sheet is going everywhere, up, down you name it.  A thin sheet even bounces during the cut.  But the result is not curved.  The guide is flexible in z axis so it just goes with the sheet and it doesn't affect the x and y axis, at least not as much as arso-bg's photes show.  This has got be happening in the x and y axis, the sheet is rotating. 

I had a problem with long sheets on the mft when I used a roller stand to support the overhang.  The mft would move a little away from me when I pushed the saw.  The roller stand wouldn't give and held the sheet so it pulled the sheet away from the fence on the mft just a little.  Couldn't figure it out for the longest time.  It seems obvious to me that something is flexing in the x and y plane during cuts.  Plus I don't think 3/4 material sitting on top of 3/4 material is going to sag from the weight of the saw passing over it.  Not enough to cause this anyway.  I bet this is x y wobble.