What's new
What's new

Masking tape on machinery - When to peel after painting?

xresonance

Plastic
Joined
Apr 18, 2018
Hi all! I'm rebuilding a 1948 South Bend model A lathe (what have I gotten myself into lol), and part of the process is a new paint job. I've got the good stuff from Sherwin Williams, industrial urethane alkyd enamel, with the appropriate primer system.

I plan to mask off the machined surfaces that shouldn't have paint on them, but I am unsure as to when is best to remove the tape - while the paint is wet, or after it has dried. Searching the net yields varying opinions, many of which say do it after the paint is dry, but all this advice is for latex paint on walls and trim around a house. The industrial enamel is some quite tough stuff, and I am concerned that waiting until it is dry will cause some of the paint skin to peel off with the tape. The only downside I can see to peeling it wet (or after it tacks up a bit) is potentially causing a mess, with the tape brushing on things. But this is easily avoided by taking good care.

I think I'm going to prep a hunk of steel and do a test both ways, but I would still love to hear your experiences with this, if you have had success or failure either way. Thanks so much!

- Aaron
 
You could upgrade to master rebuilder status and just use a broom for a paint brush. I. All seriousness you are overthinking it.. do your best to keep it in the right spot. Careful application beats masking anyday. Just have a rag ready for mess ups and have fun. At the end of the day its job is not to hold paint, but make chips.
 
What works for me is to mask up to prevent gross errors but I don't spend too long masking too closely to edges - I remove the tape once the paint has started to cure but not fully hardened - the paint on the tape is drier so its less messy. I then use a single edge razor blade to scrape off larger spots an then use the correct thinner to soften and remove any unwanted residue on those edges using a rag or Q-tip. As long as the job is properly degreased you wont have problems with peeling paint.

As the previous poster said you want to be machining not painting
 
You two make a good point, I'm likely overdoing it (not unheard of hehe). I think I'll do the cheap and cheerful quick mask, and then just paint carefully and scrape/wipe any bits that go in the wrong place. After all, this is going to be a workhorse not a showpiece! I just want it to last another 70 years so it's getting the TLC it deserves =)

Thanks!
 
Aaron, you ask a thoughtful, legitimate question. Pleased your pride in workmanship extends to a professional appearance. We finish our builds in Polane B using a DeVilbiss StartingLine HVLP gun. Use 3M blue tape. Tape is carefully pulled off as soon as done painting while still tacky. Makes for a clean edge. We don't mask threads or small holes. Find it easier to retap and use a reamer.
 
I've repainted loads of engines,machines etc. Don't bother at all with masking tape-when all is dry and cured,just remove overpaint by scraper and wire wool.
 
A place i worked at years back used to coat all of the bare metal surfaces that they didn't want to paint with grease. It worked for a quick Saturday night paint job.
 
+1 on overthinking....but since its asked, take the tape off after its dried. Don't wait days/weeks as the paint cures over time but is still quite soft the day after painting. That means easy separation of line between the paint on the work/paint on the tape
 
I wait until dry but not too many days or the tape will keep tearing.
I try to peel the tape at a backwards 45 degree (135 degree?) angle towards the painted surface.
This gives a clean line but there will be sort of a burr which you let set a little longer and a microfiber cloth can then be used to remove it.
I've gone way overboard on painting machines but I used to paint show cars.
The good thing about filling, body sanding and going crazy is that the machine cleans up easier.
When we do such I tell the guys working on it..
"Think about the fact that you are going to live with and see this work for the next 10-30 years of your life. You don't want a mistake haunting you for this length of time."
I do walk past things and remember that "Johnny" pucked that up or that "Sam" thought himself too good as a toolmaker to be doing base prep.
Not to say that I do not have a many with a simple brush on and grease with a new "dress" top coat done every few years.

In the end and the real shit and get none of this spit and polish matters to the running of the machine or making parts.
Maybe it does show a care for perfection but why would any machine tool need to look production auto level let alone concours.

All BS stuff said, do not pull wet. The paint inside has not had time to bond and will pull.
Bob
(caveat that I know only my experience, other painters will know better than me)
 
I remove masking tape after a few of hours, also done it the day after. Both have worked fine, this with 2k epoxy paint.

I think the Op is right to be considering this, when I do work like this I want it to look good. The alternative is to feel bad every time I use the machine and am reminded of how I did sub par work. I've done that before and will probably do it again, sometimes you have no choice. But it's not a nice feeling. So try to do your best, eh.
 








 
Back
Top