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Cutting Cardboard - Drag Knifes

Re: Cutting Cardboard - Drag Knifes

Postby Awesomeness » Wed Sep 03, 2014 1:55 am

The design I'm currently working with (related to the picture I showed, but different) can actually use a variety of blades. It could technically use these scalpel blades, too. The big problem is that none of these blades are the correct angle. Professional drag knives range from 30-60 degrees (angle up off table), with 45 degrees being the typical preferred angle for most work. A blade like this #10, or the Xacto #11, are closer to the 60 degree mark. That's typically only used for very thin materials, and fine work.
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Re: Cutting Cardboard - Drag Knifes

Postby bajaru » Wed Sep 03, 2014 4:36 pm

Awesomeness,
Are you not considering having a method in which the blade could be mounted at an angle? Must it strictly be mounted vertically?

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Re: Cutting Cardboard - Drag Knifes

Postby Awesomeness » Wed Sep 03, 2014 4:50 pm

Well, as you can see in the picture, the blade is really just held down with a clamping block and screws. So technically you can stick the blade in there any way you want. That's also why it has the ability to use a variety of blades, because it's not specifically shaped to only allow one blade to fit. It obviously has the ledge along the spine of the blade, to help you line up the blade straight and at the proper offset, but there is enough leeway in the design to pretty much let you do it how you want.
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Re: Cutting Cardboard - Drag Knifes

Postby bajaru » Wed Sep 03, 2014 10:20 pm

Could variably angling the blade have adverse affects on the geometry, and the tracking, etc.?
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Re: Cutting Cardboard - Drag Knifes

Postby Awesomeness » Wed Sep 03, 2014 10:43 pm

Yes, it introduces all sorts of things to account for. Angling the blade with a long skinny blade, like an Xacto #11, would almost certainly just snap the tip off right there... dead in the water. Angling a shallower angle blade, like an Xactor #19 or a utility blade, would be more survivable, but you need to put in your toolpath software how far from centerline the tip is. If you're lining it up with the spine shelf, then I can tell you how far away it is because I put it there purposefully. Otherwise, you'll be left to your own trial and error, but it is possible.

I thought about a lot of this, and my conclusion is that making it support a bunch of different blades sounds neat, but is actually (REALISTICALLY) totally unnecessary. If people using drag knives in production (see above quote from Donek) are only changing blades once per hour, the triviality of haggling over the difference in blade prices (e.g. $0.10 for utility blades vs. $0.30 for Xacto #24, etc.) is a bit petty and absurd. I keep coming back to that conclusion, even though I'm tempted to make it able to use any blade. For people in far off lands that don't have access to a particular blade, unless they are a production shop, if they order in one 100-pack they will probably lose them before they use them all up.

Right now my design is actually sitting at a decision point, because of this. I know which blade I want it to use, and they would be ~$0.35 each. If I stick with that, I can shrink the size significantly (remove 0.5" height and about 0.5" width). If I also want it to have the possibility to use tall narrow blades (e.g. Xacto #11 / #2) it needs to be the 0.5" taller. If I also want it to be able to use utility blades, it needs to be at least 0.5" wider.

Input?
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Re: Cutting Cardboard - Drag Knifes

Postby joelaw » Thu Sep 04, 2014 2:21 am

I vote for the utility blade design because they are easy to get, double ended and cheap.

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Re: Cutting Cardboard - Drag Knifes

Postby keith » Thu Sep 04, 2014 7:12 am

Utility blade please :)

Awesomeness do you have an initial "idea" of what the cost is likely to be?

Thanks for doing all this by the way :)
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Re: Cutting Cardboard - Drag Knifes

Postby Awesomeness » Thu Sep 04, 2014 5:19 pm

Boy, that's really frustrating that you guys are so hung up on the type/cost of blades. Let me rephrase the question, and see if it makes a difference, because using utility blades makes it roughly 2x as large (thus raising material and machining costs significantly).

Would you rather have (just making up rough numbers here)...
1. $60 drag knife that uses Xacto #24 blades ($0.34 per cutting edge)
2. $80 drag knife that uses Xacto #24 blades, AND comes with 100-pack of blades (probably enough for life)
3. $90 drag knife that uses utility blades ($0.10 per cutting edge; $0.20 per blade) - can also use Xacto #24, and other blades; would need to use >125 ($30 / $0.24 blade difference) in lifetime to make up cost difference!

See the problem? Do you still want the utility blades? These are probably realistic ballpark ideas of price, and the differences between price, maybe +/- 25%. The Xacto-size drag knife is small, like 1.25"x1.25", but letting it uses other blades starts making it go up to like 2.5"x2.5".

As much as I can figure, it's about $20-25 in materials/parts, plus shipping materials in, machining (current design is 3 separate setups in machining; part has to be changed around in the vise 3 times to complete machining on a standard 3-axis mill), coating (e.g. anodizing), and assembly/labor. If I did a Kickstarter for them, it would need to include packaging and shipping too ($10-15?). This is ballpark pricing without figuring for economy-of-scale discounts.
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Re: Cutting Cardboard - Drag Knifes

Postby bajaru » Thu Sep 04, 2014 7:28 pm

I'd buy #1 for sure. If it were available today, I'd send you money right now. If it were available in few weeks, that'd be fine too...

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Re: Cutting Cardboard - Drag Knifes

Postby joelaw » Thu Sep 04, 2014 8:43 pm

I would order #3 since it would 1/2 the price of others on the market. It really doesn't matter because the $30 difference is not mutch compared to tools abd bits.

Thanks for working on this.

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