trouble with miters

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photodynamix

Grumbler in Training
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Oct 18, 2002
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Green Bay, WI
I am fairly new to"The Grumble" and have been reading the posts for awhile now .. I have a problem I can not track down. I am doing contract framing for one of my customers ( I am a photographer by trade) using a double dewalt 12 chop saw system and a amp v-nailer to produce small frames in quanity. The molding I have now is produced by xylo and is about 2" wide. The frame size is a 2 x 3 inch opening. The problem is a slight gap in the inside miter. I have checked the saws, bought a sander, and checked the molding.. all seem ok. I "dry fit" all the frames before nailing and this is when the problems show up. I checked the saws with a machinest square and a 45 degree triangle but can not track this down .... ANY SUGESTIONS?????
 
Could be a number of things: sharpness and appropriatness of the saw blade, and relative humidity of the moulding stock come to mind.
If the moisture content in the stock is a little high, the drying caused from the heat from the friction of the saw blade can throw the miter off. If you are not using saw blades specifically designed for mitering wood, you may be getting some drift in the blade during the cut.
Framerguy should chime in about now, and tell you all these things in much more detail using technical language....Tom, your on!
 
The blades came with the system and at 189.00 each I am hoping thats not the problem.... but will not dismiss it. If I place 2 thickness of a index card on the miter gage closest to the sanding disk it seems to correct the problem. But like I have read on many posts, if the miter is right to begin with you should not need to sand. Makes a guy want to want to just shot more photo's!!
 
It could be caused by rubbishy cheap moulding rather than your machinery.

I have in the past been asked to remitre some of these garbage frames that the photography trade seem to love and they often seem to cut strangely or rock about which can throw the mitres off.
 
What kind of wood is the moulding? As the diameter of your saw blades increase, without blade stabilizers, the chances of "runout" will be greater, particularly in grainy pine and hardwoods.

If you are getting a gap on an image size that small, I would guess that there is something that you have missed in your setup. A visible gap on the inside of a mitered joint on a moulding 2" wide would indicate that either your saw blades aren't entering at a perfect 45&#186 or your underpinner isn't set to a perfect 90&#186 angle.

You said that you bought a "sander". Is it one that is dedicated to truing up 45&#186 miters? I can't imagine that after truing the miters with the sander, you would still be getting a bad joint.

If the saws were mine, I would first check and recheck everything to be on the money, I mean not a minute of variance to either 45&#186 or 90&#186 as applicable. If you find nothing, the next step would be to try 10" blades on the saws, although I doubt that the runout on the 12" blades would be that much unless the wood is very grainy.

Check for play in both of your saws, both at rest and at different points in their path down to the saw tables. There is an outside chance that one or both of the saws have some play in the fulcrum of the saw. These saws, commonly referred to as contractor's chop saws, are accurate enough to size a 2x4 to dimension for a stud wall. They may not do much more than that unless you tweak them to bring them into more accurate calibration.

Did you check the vertical alignment of each blade to the table. Each blade should hold a 90&#186 angle to its respective table from rest to the extent of its stroke downward.

Each of these checks mentioned have a place that you can use shimstock to correct any inaccuracies. (I cut apart a Pepsi can for a few of my shims when I tore down my Makitas and "accurized" them. If done right, you will only have to do it once.

Framerguy
 
I am by no means the one who should be answering this post ,but maybe it isn't the cut. have you checked the underpinnerer? If you apply too much pressure you can open up a weel cut miter. Also the more up to date underpinners have a rabbet support bulit in that the older ones didnn't have so when pressure was applied guess where the openning would occur?
As i said i am by no means a miter expert and I need a lot of help with any saw but I have seen what i am describeing happen with improper air pressure and settings on an underpinner.What do the experts think?
BUDDY
 
Check on your underpinner first. Too much pressure on the slide under the rabbit can cause that problem; I have had it happen. Just enough pressure to hold it firmly is sufficient. Also check the allignment of your 45 degree blocks on the underpinner; a small adjustment here can be crucial to a good joining.

Jack Cee
 
Be sure that your moulding is not "creeping" into the blade when you cut. Also, one other thing to check is if the moulding is flat on the back. I've got one moulding that I use that is not. It is the cap for a stacked set, and, if you just sit it on the saw table and cut, the mitres will be off every time. In order to cut it correctly, you have to put a piece of the bottom moulding on the saw table first, put this on top, then cut. Your problem may just simply be that the moulding is not square on the bottom, and that will make the mitre open up when you try to put it together.
 
What kind of sander are you using? Does the same problem arise if you bypass the sander? Is there still a gap if you join without the underpinner et cetera? I think one can arrive at the source of the problem by isolating the steps systematically much like one would find the problem component in a stereo system.

[ 02-11-2003, 08:51 AM: Message edited by: Al E ]
 
Photo,
Are all four corners having a gap in the inside ? If all four are it is you blade ,,, if it is just the 4th corner your 45 is off.. Sounds like you are dry fitting & the corners are off before you join.... That is a blade problem. If it was the saw 3 corners will work & the 4th is where you see the bad mitre,.. Check the inside of your cut if it has ridges (not smooth) drag your fingernail down it to check, also you can see it in the side cut on the guesso.
Try a thicker blade blank & have the blade tentioned to run at a higher RPM. Sounds like wobble or a warped blade....Gearold
 
Thank You for all the sugestions, I went over the saws again and it seems I must of got the "Bug" out. We have 175 of the 300 frames done and eveything seems to be going great, (even for a photographer who must like rubbishy frames) Again thanks for the tips!
 
I would check the LENGTH of your cut pieces very carefully! If they are off even the slightest bit, especially on small frames, you will have gaposis.
I have "production stops" that allow me to cut in a sequence like this for expample: 10" then 8" then another 10" then the last 8" - you must keep them in order and "Wrap" the moulding around the frame. I mark the ends of the joint between the first two pieces with a felt tip pen.

This will make the best possible looking frame joints, both is size, shape, color
variations, etc. I
If you cut all 10'" and then all the 8" piecews- there will be enough variation so as to produce less than acceptable frames.
 
Gregg, you are right on the money with that one. We finished all 300 frames and I had the problem of every 6 frames or so I would run into a miter that just was bad, not always, but enough to form a pattern. I would cut the 2 long legs( 2" opening) and then 4 short legs( 3" opening) and 2 long and so on. I would get to the end of a stick and need to some what match color to the next stick and proceed. These frames from separate sticks were the trouble miters but did finely correct the problem with a little sanding. I ended up having to use a little "engineering" and come up with a new clamping system other then the Phadara clamps. I went with toggle clamps and may even go to pneumatic clamps next. All and All, the client is happy and we learn a bit to speed up the process next month for the next 300 that will be a inch by 2 inch opening!
 
Susan ... I started shooting photographs for a needle art person 15 years ago, She produces kits that include the linen, needles and frames for Her creations and has shops all over the US and a few in Europe. Each month She sends out a new design and had been buying frames from a vendor for years. She had a BACKORDER from them for 18 months and got to talking to Me at a photo shoot, so I guess I now am doing contract framing for Her. The last frames were small half moon shaped, done with a router out of African Padauk wood, now That was a challenge! So the short answer is, needle art.
 
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