Machining Cured Parts

After the parts are fully cured, I need to do some machining on them for dimensional finish. I have a tool & die shop so I have milling, cnc milling, surface grinding, and polishing equipment available for the machining processes. Does anyone have experience using these processes that can help me determine the best methods to use?

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Hi I have thought about this too. I think Your biggest problem is going to be accurately entering the piece on the milling or CNC machine. My plan is to create supports that fit jigs that can be inserted into the chucks of the milling and CNC machines. If the support is entered on 0.0.0 then thats your default origin and you can calibrate the CNC machines from that start point.

@danjep: You can use any of the traditional machining processes such as a manual or CNC lathe and mill, surface grinder, and polishing equipment. It all depends on what you are trying to do to your part after post-processing. Based on my experience of the parts that I have printed, typically all I need to do is some hand sanding to achieve a proper clearance fit of mating parts. Typically I use the Clear resin, and the Formlabs resin sands quite easily. You can really remove a lot of material quite easily when sanding - - in fact, you need to be careful not to remove too much material when sanding. I use a 180 grit abrasive cloth paper for sanding. My opinion is that using a surface grinder would be total overkill.

Danjep, your question actually is a bit vague…exactly what are you trying to do to your part after post-processing? Are you trying to machine a feature that you could not print into the part geometry, are you trying to hit a tight tolerance on a critical dimension to a part feature? Exactly what are you trying to do to your part after it is printed?

Hi @danjep!

I have done some machining of printed parts. Tough machines very well, and the standard resins also machine nicely. The biggest concern with standard resin is fixturing in a way that won’t break the part or deform the part. Usually the fixturing has to be quite loose, and you need to take very light cuts because of this. If you can use double sided tape to hold parts in place, this will work very well.

As far as speeds/feeds/chip load/engagement are concerned, I would run at a moderate speed with air for chip clearing with low engagement and very low low chip load to ensure that you do not chip the part. .

When machining plastics, certain machining methods do not work well. Some plastics smear when milled or ground so I just wondered about general machining practices. Do SLA parts tend to allow milling at speeds similar to machining aluminum? When surface grinding, does the SLA grind smoothly or does the grinder cause. I can play around with some sample parts and see what works, just thought I’d see what the other users have found that works. I use emery boards for small parts since they have a coarse and a fine side. I just purchased an air eraser and haven’t tried it yet but plan to try it this week.

@danjep: exactly what are you trying to do to your part after you have cured it? Are you trying to do a skim cut on a part OD in order to achieve a tighter tolerance? Are you trying to machine some sort of feature that you could not print into the part? I believe that we can give you a more definitive answer if you can give a more definitive question about exactly what it is that you wish to do to your part after curing.

Ken, both as needed.

Hi @danjep,

In my experience, the parts will machine without much melting. Like I said above, the real limiting factor here is workholding. Are you trying to remove a lot of material?

As far as grinding is concerned, I have no idea how that will work. Sanding works well, but that is a very different abrasive process.


The basic colors machine and sand well. Tough and flexible are a bit gummy so I suspect they may be a PITA but I haven’t tried them personally.

I would advise against working with parts before post-curing, they tend to be a little gummy. I think this is mostly due to the surface of the model being softened by the IPA wash. (On the flipside of this I do any press-fits before post cure to take advantage of the slight flexibility and you can even “lubricate” the fit with liquid resin to glue it in place)

Overall the FL resins are sort of in the PMMA family but don’t behave like typical thermoplastics on account of being a UV cured resin.

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Thought I would update you on my findings. As most of you suggested the standard resins, well cured parts, do machine pretty well. Surface grinding was not acceptable, they smeared and heat warped too easily. As is well known, sanding works very well when they are well cured, so for my purposes, I will do any machining needed in either the mill or lathe, then follow up with sanding until the required dimensions and finishes are achieved. I see the Xlab printer from Italy has two resin tanks. You can have water dissolving support resin in one tank and you part resin in the other tank. Take the parts out of the printer, soak them in water and voila, no more supports. You can also have a hard resin for the main part and then the second resin can be another resin for gasket or seal areas of for tactile grip surfaces. Pretty cool.

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Hi @danjep, I googled for Xlab and found only xfab from italy which seems to support only one resin at a time, and I see no mention of two tanks. How would dual material SLA printers work? Are the resins mixed, how can they be cured differentially? Would you mind providing a reference so I can know more?

Also, would it be possible to use chemical polishing of parts like in FDM acetone is used to ABS parts? Which solvent would be a good candidate for attacking SLA resins (which are all based on acrylates, I think?).