Stepcraft vinyl cutter drag knife holder

This is a holder for a Roland type dragknife in a Stepcraft cnc. Two parts are printed, the 43mm cylindrical holder…
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updated April 30, 2022

Description

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This is a holder for a Roland type dragknife in a Stepcraft cnc.

Two parts are printed, the 43mm cylindrical holder for the Roland dragknife and the screw down clamp that keeps the dragknife in the holder with some spring pressure.

These dragknives are designed so that the face slides over the surface held there under pressure from the spring. The depth of cut is set by how much the blade protrudes from the knife holder, adjusting the screw section at the top of the knife to just cut the vinyl, not all the way through both the vinyl and backing.

The spring applies constant pressure (and helps to protect the knife if you should crash into the bed), it allows the whole dragknife to recede into the holder a short way. To adjust the pressure use a different spring or compress the spring more or less by screwing the clamp down more or less.

You still get access to the ejector pin but to adjust the length of the blade that protrudes you need to remove the knife completely because the locking nut is inside the clamp. This shouldn't be necessary if you use blades that are all the same length.

Remember to smooth the end of the aluminium holder so that it doesn’t grab the vinyl as it glides over the surface, do this with the inner section removed to avoid getting grit in the bearing, remember to clean it out afterwards. My new dragknife was rough to assemble because it still had chips or grit from when it was made originally, some cleaning alcohol and new light oil improved it significantly.

Thread matching:-

The threads in the holder and clamping lid are designed using Fusions thread function and the fit may be too tight after printing. I scaled the clamping lid X and Y by 98.5% in the slicer to make it just a bit smaller to ease the fit.

My spring has an OD of 14mm and the wire section is 1mm. The whole spring is 3 coils of uncompressed length 12mm. The spring just needs to be a close fit around the knife (1/2" ID).

My model of the Roland-style knife is measured from one I bought online. I guessed at what was inside the screw in part and I didn't include the bearing. Yours may be different depending on the manufacturing "quality".

An excellent informative tutorial on vinyl cutting with your CNC can be found here.

A video about setting up the drag knife.

And this one is very good, has a few important tips.

And Lars Christensen has a very clear video for Fusion users and Stepcraft’s own drag knife but all the information is valid

You will see some designs are rigid or have a spring press on the ejector pin, those might be troublesome if the whole knife can't move.

Print Settings

Printer Brand:

Creality

Printer:

Ender 3

Rafts:

No

Supports:

Yes

Resolution:

.2mm

Infill:

35%

Filament: Amz PLA Orange


Notes:

Print the holder upside down with circular supports touching buildplate, the supports will easily come out of the recess with the threads. Print time was about 1hr 40 minutes.

The clamp should be resized by the slicer in the x and y by 98.5% to allow easy thread engagement.

Print the spring clamp with the threads up. No support will be necessary. Print time is less than 40 minutes

Post-Printing

Depending on how big the z-seam bumps are the knife may be very tight. The centre hole will need to be filed or sanded. Keep going until the fit is loose enough to move if it crashes into the bed but still snug so the knife doesn't move around as it cuts. I had to do very little filing and the knife shows almost no movement sideways

If the lid is too tight around the dragknife lock-nut and back adjustment nut, it too will need to be filed. This is less critical but mustn't allow the spring to pass when assembled.

Some light silicone or white lithium grease on the threads always helps.

If the holder is too loose in your spindle mount then add some aluminium tape around the circumference. Kapton will also work. I sized it to be the same as my HF500 spindle - 43mm.

Category: Machine Tools

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The author marked this model as their own original creation. Imported from Thingiverse.

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