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Mitred Boxes

7/22/15       
Richard

Hello all,

I have a customer who needs to produce a relatively large quantity (300) of the attached display unit in the attached drawing. They will be made from 3/4" thick maple veneer. The only difference from the drawing is that the boxes will be made with a mitred joint rather than the butt joint that is shown.

My question before they get into it is what the best approach is? They have a CNC and sliding table saw. Originally when it was a butt joint I was thinking we would cut everything on the CNC with blind dadoes. Now with it being mitred I am leaning towards ripping lengths on the saw that are the depth of cabinet. Edgebanding and then cutting the mitres. my main concern is that there is a single man in the shop and I am not sure how well he will be able to maintain accuracy with that volume of work.

Do you think it maybe possible to rip the sheets on the saw and edgeband. Then set the parts on the CNC to run the mitres? I have mitred MDF before pretty successfully but never veneer.

Any thoughts are welcomed.

Richard


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7/23/15       #2: Mitred Boxes ...
david

Richard,

I would run samples using the CNC to do a miter fold. Cut the material to width, edgeband, and then have the miter folds run on the CNC.

I had a mobile pedestal (18" wide) that had an angled back on it to clear metal support under a desk. We used a miter fold for the top panel, angled back, and the back panel.

It takes some trial and error getting the correct depth, but once you find the peaceful medium, it works like a charm.

7/23/15       #3: Mitred Boxes ...
Richard

Hello David,

Do you cut through the veneer or actually fold the veneer itself?

I am also wondering about the possibilty of doing some kind of locking mitre. Any thoughts on that?

Thank you

7/23/15       #4: Mitred Boxes ...
james mcgrew Member

Why not build the boxes butt joint, pocket screw and veneer the ends, strong easy

7/23/15       #5: Mitred Boxes ...
Richard

Yes James that does sound like a good solution to. Unless they specifically want to see mitred front edges.

To be honest with you I am a little unsure as to what the exact situation is. I am freelancer draftsman and programmer for this customer. Typically this is not the kind of product they manufacture (Mostly kitchens) and they are attempting to match a sample.

If I was in a position to have a conversation with the end user I would be making suggestions in order to make production more efficient and would see what deviations from the sample would be acceptable in order to facilitate that.

At this point I have to work with what my customer is telling me and try to figure out the best way to build it based on those parameters and the strengths and weaknesses of his shop.

Thanks again

Richard

7/23/15       #6: Mitred Boxes ...
james mcgrew Member

If you have a really flat table you can use a 91 degree v bit and make the entire box by pre-edge banding the individual strips. key is flat bottom

7/23/15       #7: Mitred Boxes ...
james mcgrew Member

I have a friend who makes these for the large Panty company, he is quite successful at it.

7/23/15       #8: Mitred Boxes ...
Bob Harkleroad

:^)

7/23/15       #9: Mitred Boxes ...
Larry

I'd consider doing lock miter on the shaper. You will need to pin wheel the lock miter to keep from blowing out the banding. Each part has one edge run flat and one run vertically. The catch is that the top/bottom are too wide for the feed on the shaper and you will need to devise a way of holding them against the fence. Simple solution is to mount a feed to the front of the table for the one edge of the tops & bottoms. Once setup & tested the process should be very quick. Of course using two shapers would be nice since batches could be any quantity. Miter folding also works, you just have to set the router so the bit doesn't quite go through. New, freshly machined spoil board! Ideally the tape would go on first. Know anyone with a miter fold machine? Probably the cheapest solution is to have all the parts made by someone with such a machine.

7/23/15       #10: Mitred Boxes ...
Richard

Thanks for the responses.

I have found a couple more facts out. The backing has been eliminated, apparently they are just using corner braces and the will be using a ply core. They are unconcerned with the grain matching at the mitre.

I think that I am leaning towards mitre folding the parts. The main issue is that the dimensions will not fit yield well on 4x8 or even 4x10. The largest box ends up being 102 1/2" when flattened and the smallest is 72 1/2". I can get a better yield if the parts are nested to maximize material usage but in this case I have to cut clean through the veneer as the parts will be not be laid out unit by unit. In this case can I still use an insert type v-groove router tool to cut through without tearing out the end grain? Will I have to apply tape were the cuts will be before I machine, then remove it and apply more tape before folding?

They do have a shaper but it has no feeder and they do not seem very competent with setting it up. The other thing is if it's a locking mitre it would have to be blind. I figure this could be done on the CNC with multiple tools as I could stop the lock mitre tool before it cuts through the edge and then clean up with the folding tool.....As I am writing this it seems like I am over complicating!

Just trying to weigh up what method is best.

Richard

7/23/15       #11: Mitred Boxes ...
Larry

Seems like the CNC miter folding is the simplest solution. The problem with a "V" bit is it has almost no velocity @ the point and if you cut the last few 1000ths all the way through it may want to tear the end grain. With the tape in place it will help a lot. The only parts you will need to remove the tape from are the odd parts required that can't be continuous because of sizes. Not a big deal just put new tape on the other 3 parts matching edges and carefully place the odd part. You may want to make some support pc. to help while gluing up. You are going to need to edgeband after glue up most likely. I'f try it first with already banded strips on the router but it will probably want to pull the tape lose on the side of the bit rotating away. The ideal is to use a V shaper cutter always cutting into the banding. They make aggregates for that to use on the CNC, expensive! Another possibility would be to miter them on the radial arm saw with an inserted shaper type head. Requires a good saw, perfectly set up & a set of spacer blocks to position the work.

7/23/15       #12: Mitred Boxes ...
Richard

Larry-

I am not sure about banding them after the mitres are cut. I was planning to rip 4'x8' sheets to 20" wide lengths then band them. I will secure an MDF strip to the spoil board which the banded lengths will be pushed up against to prevent the banding tearing out. Do you think this will work?

Now if we do go with a V- Groove router do you think it's best to go with a true 90 deg. angle or the folding bits that are slightly more? In the past I have always found the true 90 deg. yield the best result. Just wondering what the consensus was here?

I had thought about an aggregate tool with a shaper type head but I don't think the project will justify the expense.

The radial arm saw is an interesting idea, but I am unsure if it's faster or more accurate than a sliding table saw?

7/23/15       #13: Mitred Boxes ...
Larry

A slider seems like it would take a lot more time. I've used bot the 90 and the 91+- bits, didn't see a lot of difference for what we were doing. In theory the 91 degree bit should produce a tighter outside corner.

The backup strip should work if you can hold everything tight enough. Need some way of compensating for minor variations and to be able to hold pressure while cutting.

7/23/15       #14: Mitred Boxes ...
Richard

Larry-

I was thinking that a strip would be secured at the back of the CNC, The 20" lengths would be shoved against this and then have another sacrificial piece suctioned down along the front edge. Does that sound about right?

I guess I will stick with 90 then as we will need a good inside and outside corner as the box is open.

Thank you for your thoughts!

7/23/15       #15: Mitred Boxes ...
james mcgrew Member

91 degree assures fit and some glue space

Amana tool cnc insert miter fold shank

7/23/15       #16: Mitred Boxes ...
rich c.

I've used that Amana bit, but didn't like the fit. I loosened the insert bolts, and inserted a thin piece of paper near the end of the cutter, between the carbide and the bit body. Tightened the bolts and the shim stayed in place and gave me a better miter. The insert is really sharp and gives a good cut at the point. I built a fixture with fences front and back. Slid the stock in the fixture and clamped down. The fences eliminate tear out.

7/25/15       #17: Mitred Boxes ...
rich c.

I reread my reply, and I wanted to clarify where I put the paper shim. It is not on the back face of the carbide, it is between the edge of the carbide and the locating face milled on the cutter. It is used to space the carbide slightly off the ledge to reduce the angle of the cut. Sorry.

7/26/15       #18: Mitred Boxes ...
Brian T

I mitre fold boxes every day on the CNC.

We use MDF, Veneered MDF, ply and solid stock. I do not use 91 degree bits on stock over .25'' or on any material that needs a tight inside joint. I have amana and vortex bits. The vortex is just slightly over 90. With MDF I run the same bit twice. First pass on .75 material is .69 and the second pass is .74 if I'm doing a true pre taped mitre fold. If we are cutting parts out then taping after I run the bit down to .752 to get better tip speed.

With ply core I use 2 seperate vbits. I use one to hog material and run it to .72 and use the finisher at .74. This will result in a much cleaner cut.

7/26/15       #19: Mitred Boxes ...
Brian T

I forgot to add. If I was running these boxes I would rip lengths on the saw first, edgeband then put on the cnc for folding. I would nest 2 of the programs at once leaving 4-5'' between the 2 cut paths. First I run the program with a .375 down cut around the outside of the part to give me the 2 outlines. Then I delete the tool path and save it as vbit path only. I take scrap and pin or screw to my spoilboard so parts are always in the right place. Also these boards stop the banding from blowing out. When I make the program I run the toolpath 1'' beyond the edge of the box. I break the path in the middle and run my bit from the outside of the part to the middle of the parts. This seems to create less tearing of the banding however a little clean up with a knife and a block of wood and sand paper is still necessary. While 2 boxes are being cut out my operator is assembling the 2 previous cut boxes.

Hope that helps.

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