Flatpack Slots and Tabs

[zorlack]

Ok,

So here's a process question for those of you who do slot-together designs:

When designing a piece of furniture (or whatever) that fits together using slots and tabs, its necessary for me to know the dimensional thickness of the material. For example, the 3/4" plywood that I'm using at the moment is about .717" thick. Though sometimes the sheets seem to get down into the high .6's.

So the question is, has anyone devised a method for making readily adaptable models that can be quickly changed to accommodate different thicknesses? This problem also happens when doing prototyping. I can scale the cut-file down as long as I have the right diameter bits, but I couldn't really get any accuracy in the slot dimensions.

One of the things I've been thinking about is creating a set of intelligent blocks in Autocad that represent the slots that I need to cut. Then I can change the blocks globally. However, I'd still then need to take my design into Artcam and redo all the tool paths.

Does anyone else have a solution to this? Am I making it more complicated then it really is?

-D

[landdesign]

dave

your not making it harder than it really is. I work with this every day and have yet to get an adequate solution. the plywood in my area varies up for.080 for sheet to sheet, usually though only .015 is the norm. I scale all my drawing masters to .75. when I cut I have to see the sheets and scale to what I have on hand in sheet goods. as you can see this isn't the greatest way because if you are trying to maintain an exact overall part size the part will scale with the scale of the slot. I tried the idea you are thinking about , but then you run into the troubles of making sure the slots maintain the proper relationship to the connecting tabs. I know a friend that instead of designing a slot that is an integral part of the profile, he inserts a center line mark and then can put whatever size slot box over that. it still isn't a great solution to the overall problem of lousy sheet goods.

Erik

[zorlack]

Its also an interesting problem because its more than just about lousy sheet-goods. Lets say I make a chair out of 3/4" ply, but then I want to make my chair into box-kite out of it by cutting it out of something ridiculously thin.

You're right about the problem of choosing correct registration points for the tab location being a doosy. Sometimes you want the slots to always be on the outside of a model, sometimes you want them on center.

Its almost like the slots/tabs want to be a completely different set of cutting instructions, but I'm not sure that makes any sense.

When you use 3/4" as your slot basis do you find that the fit is usually acceptably good?

[landdesign]

Dave
I use 3/4 as the master drawing scale only... its not to often I cut a slot 3/4. here in Oregon it seems .71 is a pretty good average for the prefinished plywood I use. I usually buy by the unit and see what I have for size. I try and go ply + .010. its a pretty good fit and allows people to take apart and put together without too much grumbling. fortunately the stuff i make in flat pack doesn't have hold real tight tolerances. I'd like to know how the large company's like Ikea deal with this trouble when they cut 10,000 units on an item?? do they get better goods when they buy 80 units of plywood at a time?


Erik

[zorlack]

Ikea's stuff is mostly veneered MDF anyways, so when they ask for 70mm sheets (or whatever), they get 65mm of pulp with 5mm of melamine (or whatever).

I think plywood varies differently from the more synthetic materials.

[erik_f]

On some cuts and joints this won't be a option, but if you were to zero from the spoil board, and you were using a good hold down method such as vacuum, it might be worth trying to not only mill out your slot, but mill down your tab to the desired thickness. I am right there with you guys and this just came to me while I was reading the posts. The problem with this method is it would only work a portion of the time.

[sneakers]

As you can see by the number to the left this is my first post and I am just a beginner at this. I have been playing with this exact problem for the past few days and have come up with a possible solution. Eric said his average thickness is .71 and his clearance is .010 so combined he should set his thickness for .720. If his material is plus .020 he can use a bit that is .010 larger than his normal bit and keep his settings and the slot will be .020 larger than his usual slot. If his material is thinner he uses a smaller bit 1/2 the difference. I measured my bits and I cannot find 2 .25 bits the same diameter so using bits a few thousands off is not a problem. As I said I am just a beginner so I might be way off base but this works for me.
Gary

[kirkkelsey]

We do our designs with the Parametric program Alibre Design and set a parameter for the material thickness. This allows us to input the material thickness and have the design modify the slots to suit.

Where Alibre differs from AutoCAD is in the case where the dimensions drive the design, rather than report the set dimension.

[rhfurniture]

Depending on software, can you not designing to the maximum sheet thickness, then adjust machining offset to allow for the material - your overall dimensions will only then be a tad out.