Overcuts on inner mount window

[Will Niekirk]

I am an occasional framer so please forgive me if this first post is a dumb question.
I cut a double mount recently - taping the inner mount to the outer mount (once it's been cut) and then cutting the inner window. The registration was perfect as it should be, but I realised when I looked closely that while the outer mount had cut correctly, the inner suffered noticeable overcuts in one direction on all 4 corners. Both mat boards were identical (2000 micron, or just over 1/16th of an inch).
In the past I've had to adjust the under / overcoat settings when changing from thinner to thicker mat boards and vice versa, so I wondered if this was happening because the cutter (keencut ultimat gold) sees the board as twice as thick as it is, because it's effectively two boards thickness from the cutter base.
I guess I can always cut smaller test windows in the inner mount in future to adjust the cut length before committing, but that's quite a long-winded process and the demos I've seen don't seem to have this issue.
Any advice welcome!

 

[wpfay]

Hi Will, and welcome to the G.
A couple questions first:
Assuming you are using production stops for cutting the mats, and that the fallout is taped back into the 2 mat stack.
Is the overcut on the entry or exit point?
Do you make any other adjustments between cutting the top and bottom mat other than adjusting for the mat opening?
How much is the overcut?

Both entry and exit points will vary in this instance.
As far as I know, there should be no blade adjustment between the two.

 

[Will Niekirk]

Hi, and thanks for replying. Assumptions both correct. The overcut is on the exit (end of cut) and I don't make any other adjustments apart from the stops to change the opening size, and the size is just right. Overcut is about 2mm.
It's a second-hand cutter and as mentioned I have to adjust the over and under cut settings on the stops for different thicknesses of mat. I was wondering if that's normal.

 

[Prospero]

This can be a bit mind-wrangling....

If you have the blade extension set correctly then the far (entrance) production stop is set for 1.5 thick board then that
will be true for any thickness. BUT the near (exit) stop will need recalibrating for thicker boards. The extra blade extension
compensates when you plunge but at the other (near) end it will need to go further the thicker the board is.
So if the upper layer board cuts true the the lower one should do the same. It doesn't matter if there are two thicknesses
when you cut the lower layer as the reinserted dropout is acting as the 'slip sheet'.

Sorry for the lame non-answer but it's hard to tell what going wrong without watching you do it.

 

[Rick Granick]

Are you sure you set the stops accurately when adjusting for the second cut?
Rick

 

[Will Niekirk]

Are you sure you set the stops accurately when adjusting for the second cut?
Rick

Well, I guess I can't be sure as the moment is passed! But the size of the inner window is correct and the alignment is as near perfect as I could want - the technique definitely works in that sense, so I don't think it's the stop adjustments. But as the previous commentator mentioned, it's a bit mind bending indeed, and I will pay very carful attention to this aspect when I try again. Thanks a lot.

 

[Will Niekirk]

This can be a bit mind-wrangling....

If you have the blade extension set correctly then the far (entrance) production stop is set for 1.5 thick board then that
will be true for any thickness. BUT the near (exit) stop will need recalibrating for thicker boards. The extra blade extension
compensates when you plunge but at the other (near) end it will need to go further the thicker the board is.
So if the upper layer board cuts true the the lower one should do the same. It doesn't matter if there are two thicknesses
when you cut the lower layer as the reinserted dropout is acting as the 'slip sheet'.

Sorry for the lame non-answer but it's hard to tell what going wrong without watching you do it.

I see what you mean - so it shouldn't be different between the two boards. No matter, food for thought in both blade extension and stop adjustments. I think I'll do some experimenting and see if I can reproduce the error - or even better, not!
Thanks for the advice.

 

[artfolio]

This is a stab in the dark but when you cut the second matt do you remove the slip sheet you used for the first one? If you don't that the resulting triple thickness will definitely throw your cut off. (Don't ask me how I know this )

 

[RoboFramer]

This simply shouldn’t be happening. If the top mat cut OK then the bottom one should too.

You mention registration, so I assume that means you’ve cut both boards the same size.
Don’t do that, cut the bottom mat a fraction smaller than the top one, use dots of PVA along with just a dab of DS tape each side to keep things still while the PVA dries. Just make sure there’s no adhesive near the reveal area!

This means there is no registration required, bottom mat sits JUST inside the top mat and all
the guides and stops are, no argument, using the same board as they did first time round.

 

[Will Niekirk]

This simply shouldn’t be happening. If the top mat cut OK then the bottom one should too.

You mention registration, so I assume that means you’ve cut both boards the same size.
Don’t do that, cut the bottom mat a fraction smaller than the top one, use dots of PVA along with just a dab of DS tape each side to keep things still while the PVA dries. Just make sure there’s no adhesive near the reveal area!

This means there is no registration required, bottom mat sits JUST inside the top mat and all
the guides and stops are, no argument, using the same board as they did first time round.

Well I’m with you there - it should not be happening!
Probably using the wrong language, when I said registration what I really meant was that the inner and outer windows ended up exactly the right size and in alignment with each other, just what I was aiming for, and to achieve that I was doing as you recommend, using a slightly smaller board for the inner mount. Just getting that annoying overcut on the inner one.
Thanks for the advice though!

 

[Will Niekirk]

This is a stab in the dark but when you cut the second matt do you remove the slip sheet you used for the first one? If you don't that the resulting triple thickness will definitely throw your cut off. (Don't ask me how I know this )

Ah, your stab in the dark may have hit a target! No I didn’t remove it, I left the slip mat in place, so yes I guess that makes a triple thickness. I won’t ask how you know (!) but I’ll give that a go. Thanks so much.