Finishwork on FDM Parts

Date: Mon Apr 01 2002 - 17:33:48 EEST

Again I'd like to thank everybody for your help. Some of you were asking me
to be more specific as far as what I found out. I'll give it a shot.

One method was to dip FDM parts in a solvent such as Methylene Chloride,
MEK or acetone. This helps the layer lines to "run together", smoothing out
the surface. This can be done with care, but you do risk warping or
damaging the parts if they are thin walled or have small features,
especially if the parts are in the solvent too long. Also the part may need
to dry for awhile before working with it.

Another is to spread, rub or wipe these solvents on your parts using a
paint brush or towel. We've used this method with some success. Small or
delicate features must be treated with care. Also be careful what brush or
cloth you use. The solvent may attack the brush or towel causing it to fall
apart and stick to the part (make sure the towel is saturated). In both
these cases remember that you are working with strong solvents. Work in a
well ventilated area or use a respirator. Also wear heavy rubber gloves,
not Latex or Nitrile.

A third method is to sand the parts out as best you can using 60 grit or
coarser sandpaper. Hope you have strong hands and don't break your parts!

Finally you can use any number of fillers to fill in those layer lines.

I don't want to sound overly critical of FDM. I think it's a great process
and we use it regularly. Our modelbuilders are able to make some great
looking models using FDM parts. It's that a similar part CNC machined out
of ABS usually requires little more than sanding lightly with 180 grit
paper and it's ready to be painted. No need to take the extra time and use
caustic solvents to aid in finishing. If Stratasys (or anyone else for
that matter) developed an ABS plastic that was more like the blends
available for machining, we would definitely make more use of it.


Robert S. Gansen
Johnson Controls Inc.
Automotive Systems Group
915 E32nd Street
Holland, MI 49423
Tel: (616)394-8095
Fax: (616)394-1166
Pager: (616)670-8095

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