Different Density of Foam vs Grit Size Dremel Bits

Here to answer some of the common questions such as: why is some foam more expensive than others? Does the quality get better with cost? How will the different grit on sanding drums affect the finish?

Summary

There has been a lot of recommendation for stone tips but is this the tip that trumps all? Should we scrap the use of the sanding drum all together? I've done some basic testing and noted down some of my thoughts on each tip. Hopefully, it'd help someone decide which one tip to use.

The tests were done on 3 different types of foam and different thicknesses. I tried to keep the pressure and times similar so it would be as controlled as possible.

Disclaimer: I said I tried but didn't actually try that hard...

Density Tested

Craft Foam, CF65, CF100

Thickness

5mm, 10mm

Dremel Bits Used

120 grit, stone tip

Sanding Drums

There are many types of sanding drum but as a primary rule for foam, the larger the number the smoother the finish. The default sanding drums from Dremel is usually around 60-80 grit. They are good for hacking big sections off the foam but doesn't provide a smooth enough finish. Personally, I start with a 120 grit drum and never change it. The grit will ware down and it'll naturally turn into a higher grit drum.
As a personal preference, I normally hack off as much off as I can with a blade and keep sanding to a minimum. I found this method is more controlled and there is a less chance of over sanding. As for the size of the drums used, I prefer a slimmer tip rather than a lot of girth.

Stone Tip

There are many tutorials out there that would say "only use stone tip" but just like anything else, there is a time and a place for everything. The problem with stone tips is that while it gives a smooth finish for a small area, when the tip heats up, the foam tends to get a fluffier finish when used against less dense foam.
Experiment with the different stone tips. Not only can they sand the foam down, they also produce realistic rivets. I would recommend using a Dremel Workstation for this as it gives more control.

This is probably the most obvious contrast between a sanding drum and the stone tip.

Sanding Drum 120 grit

Even with quite an old drum, it still looks rough like the skin on my face.

Stone Tip

Although it looks much smother, if the stone tip overheats due to excess usage, it'll create a texture similar to the sanding drum. A heat gun will not really remedy this as this type of foam expands ever so slightly rather than contracts. The best solution is to use 1000 grit wet/dry sand paper and hand sand it back down.

This type of foam has the closest density to floor mats and reacts better to heat than the budget Craft Foam.

Sanding Drum 120 grit

The foam gets increasingly less fluffy as the density goes up. Heat does help reduce the fluff a little. It is better than nothing.

Stone Tip

Stack is built with customization and ease-of-use at its core — consistent markup and useful data attribute modifiers make rapid development simple.

Sanding Drum 120 grit

Combine blocks from a range of categories to build pages that are rich in visual style and interactivity.

Stone Tip

Still a visible improvement over sanding drums. This time however, the heat will add to the smoothness as this type of foam contracts on heat more so than the previous densities.

Additional Notes

On paper and images, there seems to be a clear winner in the stone tip vs sanding drum battle. However, we did not fully explore the practical use of the types. The stone tip is fantastic for fine-tuning and finishing seams but it doesn't do as well with sculpting or shaping.

The sanding drum is brilliant for shaping pieces and detailing. Be gentle and careful as one mistake may leave you with an undesired grove.

Personally, I find it a lot easier to control the tips when going with the rotation rather than against. Pretty much the opposite of woodwork.

Have you considered...

Using wet dry sandpaper for seams? It functions the same as a poor man's version of the stone tip but it offers a little more control and does not overheat. Because I've a lot of practice on the sanding motion, having been a teenage boy for a number of years, I always finish my builds with a good rub with the wet and dry.