Sunday, September 24, 2017

Pumprake with swappable 3D printed rake adapaters

Halloween is about a month away and stores will be lined with these electric pumpkin carving tools.

I thought it was time I revisited a project I started Halloween of last year. The below is the story and build, but the TL;DR can be found in this video.
I created a 3D printed part that allows you to swap rakes in the Pumpkin Master electric pumpkin carver.

You can check out the video then jump to the STL file and print your own: 

You can find the Pumpkin Masters electric carving tools on Amazon, but I generally find them cheaper at CVS and Walgreens.

Want to know more, keep reading after the break.


Almost a year ago I saw this Tweet by @indiecom showing @jimylongs modified electric pumpkin carving saw that was turned into a power rake. It was dubbed the pumprake or pumpkey depending on who was commenting. I am still not sure of the official name, but I liked pumprake -

I wanted to make one, but I also decided I wanted the rakes to be interchangeable. How could I make it easy to swap a city rake for a wave, etc? I went online and found one of the electric pumpkin carving tools and noticed each saw blade had an identical small plastic end. I could model this in TinkerCad to create an adapter for modified rakes in the electric carver.

After much consternation with a set of calipers I was able to model and 3D print the plastic end for the saw blades. These can be used to hold modified rakes making them interchangeable.

Just in time for Halloween I’ve tested the parts on the old version and new version of the Pumpkin Master carving tools. You should be able to find these carvers wherever fine Halloween gourds are sold.

Check out the video above. I also documented the build process in this blog post. If you are just interested in the STL file to make your own click here. The STL can be modified in TinkerCad, printed at home, or sent to services like Shapeways for printing. I use TinkerCad and then send it directly to Shapeways for printing from inside the TinkerCad interface.

Happy Halloween and Happy Picking! Tweet @eanmeyer to let me know if you print the part and how it worked for you!

Build Process


First, I spent a fair bit of time measuring all the nooks and crannies on this tiny part with a set of digital calipers.

My trusty-ish Harbor Freight digital caliper and Moleskine and some whiskey (not pictured).  


Fast-forward many hours in TinkerCad and we get the 3D model. Yes, this is very much a “draw the rest of the owl” moment. However, I am publishing the STL so you don’t have to go through this part of the build. 

You can jump right to my TinkerCad build here: 

Send to Print

I like TinkerCad because it directly integrates with Shapeways. I don’t own a 3D printer. However, I’ve sent many parts to Shapeways for printing. You can see this part was successfully printed once. Shapeways will take about a week to get you the part. The part arrives laser sintered and aren’t made via the filament printing process.

A Wild Part Appears

About a week later the parts showed up. 

Because they are laser sintered the small hole the rake will go in often has powder packed into it that needs to be cleaned out. Use a pin or needle to clean this out by scraping out a bit at a time until you can see through the hole.

You can see in the photo where I am holding it the slot is hard to see. Look at the 3D render to see where the hole is more clearly.

There may be loose material in the hole you need to clean out with a pin. 

Preparing the Rakes

Now we need to measure the tools. The 3D printed part has a hole running through it to mount the rake in. This means we need to cut away some material from the rake. 

I took some measurements to grind down the rake. The internal measurements of the hole used to mount the rake are approximately 18mm x 2.75mm x 0.55mm. After marking off the metal to grind away we are ready to head to the garage.

Metal Work!

Next, comes some metal work. You could do this with a small metal saw and file if you don’t
have power tools. However, I used a bench grinder and angle grinder to modify the rake.

I’m not sure which approach would work better, however, I used the bench grinder first as it conveniently makes a right angle for me when grinding away material. 

However, you could use the angle grinder to cut off most the handle first. Take your time with this part and have a plastic cup with water or cooling oil near by to dip the part in. Too much grinding can warp or weaken the part.

Now we use the angle grinder to cut away the handle. 

You can see my now separated pieces on the bench.

Back to the bench grinder to take the burs off.

Finally, we take the end that will get inserted into the 3D printed part and taper it into a knife like shape. 

I choose to think of it like one of the plastic cocktail swords you find in drinks. This shape will allow you more easily insert the rake into the adapter. 

This is a lot like the tang on a blade fitting into a knife handle.

Fitting using your Imagination

This is where I don’t have photos because holding a hammer and a phone became… problematic. I will likely print a few more and update this with a photo or two. However, the below should describe the process adequately. 

The final step is to mount the rake with the rake end inside of a bench vice. If you don’t have a bench vice a wood clamp secured to something sturdy could work. After securing the rake with the “tang” side up gently tap the adapter into place with a hammer.

If you removed too much material from the rake use 3D print safe glue on the rake, insert into the adapter, and let it dry.

Try and get the rake “tang” all the way through the 3D printed part. You can see in the video how my first city rake is wobbly because the part isn’t fully seated. The triple peak rake in the video doesn’t have this issue.

Finished Product
At this point the rakes should be ready to use! The new rakes should insert in the exact same way as the saw blades. 

As mentioned in the video I tried these in both the new and old version of the Pumpkin Master electric saw. Hopefully it works for you too!

Tweet me @eanmeyer to let me know if you used the part, how it worked, and if you have any suggested changes.