paint prep - part 2

Cal Haines · Sep 4, 2008

[continued from http://www.practicalmachinist.com/vb/showthread.php?t=159301&page=3]

I haven’t been able to spend much time on the paint job in the last two months, for various reasons, but I’ve been pecking away at it. I’ve finished up with the base filler and have the high fill primer on now.

As I said in the previous thread, I decided that the 4+ layers of old paint on the headstock and gearbox had to go. There was just no way to get a decent result with all the layers of hastily applied paint on the many compound surfaces.

Here’s where I wound up after stripping the headstock and gearbox, primarily with 2” Scotchbrite discs on air tools:

One problem that I didn’t properly appreciate was the lump on the rear half of the headstock casting, over the spindle. Here’s a photo with a piece of steel strapping bent across the top of the casting. You can see that the left side is lower than the right (back) side. I suspect that something happened to the pattern position when it was being rammed up:

I had initially thought that the left (front) half was low and decided to fill it to match the back. But on closer inspection, it’s the other way around. A very crude grinding job was done at the factory to blend the casting to the front bearing retainer ring. I decided not to try to grind the casting to the correct shape; I just don’t have the necessary skills. Instead, I opted to fill the low area and try to blend it together.

I took DaveE’s suggestion to use Evercoat Rage body filler. It’s only available in gallons, but I was able to get partial can, about a third of a gallon, from a local body shop. It took about 4 hours to coat the headstock and gearbox. Most of that time was spent mixing filler and cleaning up tools between batches. It took me 20 to 30 minutes to mix a batch, apply it and clean up for the next round. I used a digital scale to help control the proportions. You’re supposed to mix 2% hardener by weight. I wound up using 25 to 30 grams of Rage with one drop of hardener.

Here’s a photo with most of the first coat of filler on:

Mostly out of ignorance, I proceeded as if I were icing a cake. Instead of the paper-thin layer that I had imagined, I wound up with an eighth inch or more in some places. The problem was compounded by ridges and high spots on adjacent patches which would lift up the putty knife and make the thickness even greater. (It’s definitely a good idea to trim those things off while the filler is still soft; something I didn’t do).

In retrospect, “icing” a lathe is a very poor way to proceed. I had done something similar with the Bondo 902 putty on the base and it was easy to sand down the high spots. Not so with the Rage! It took me 4 hours alone to just trim and file off the high spots so I could start sanding:

The headstock upper cover had been powder coated and all of the grain of the casting showed through. I decided to paint it as well and was pleasantly surprised how smooth the powder coating sanded out. It apparently makes pretty good high-fill primer.

It took another 15 hours of tedious work to finally get to a point where I just had filler in the low spots:

I wound up using just about every small sander I own, including a Dremel-type tool with a small diamond plated ball for the small radii:

… and an assortment of sanding blocks, dowels, scrapers, and the like:

I learned a few things along the way. If anyone is interested in more details on the sanding part, just say so and I can elaborate.

It took another 11 hours to apply 3 more coats of Rage to low spots and sand. I spent a lot of time trying to blend the headstock upper cover to the headstock. The Rage isn’t very good near sharp edges, so I used JB Weld to fix a corner that had broken off of the cover.

Re-masking for primer took another 3½ hours. One of the most tedious parts of masking is all the small round things like bolt heads. I solved that by putting masking tape on the backing paper from Avery labels, then punching various diameter round masking tape disks with a gasket punch set. (Slit the backing paper before you apply the tape.)

Here we are ready for primer:

A pencil sharpener and a length of dowel are handy to make plugs for small holes.

[to be continued…]

Cal

DaveE907 · Sep 4, 2008

That shows real perseverance Cal! I can appreciate all the work you've put into getting to where you are, it's looking good.

One tool you don't show that would make your work easier and faster is a Stanley 10" Surform half round regular cut replacement blade. They're often called "cheese graters" around body shops. Here's a link:

http://www.stanleytools.com/default...174;+Half+Round+Regular+Cut+Replacement+Blade

These are used without handles to rough shape filler during it's hardening process. Apply the filler and when it reaches the consistency of hard cheese (hence the nickname) use the Surform to knock down high spots, ridges and to do the rough shaping quickly. Do this after each application of filler before applying another layer and you'll avoid a lot of work shaping the hardened filler in subsequent operations.

Here's a photo of using one from about a year ago. It also shows another shape of Surform, a full round. IMHO these are the two most useful shapes.

G1K · Sep 4, 2008

It's starting to come together, very nice work Cal. I'm looking forward to the next installment.

Ryan

Cal Haines · Sep 4, 2008

Dave,

Thanks for the tip. I thought about getting one of the Surform files, but my Dad’s old rasp, visible in the forth picture, did a pretty good job on the curved surfaces.

Does it look like I got too much filler on in the first application?

Cal

Cal Haines · Sep 4, 2008

priming was an adventure...

(I’m going into a lot of detail here hoping that it will help the next rookie; I certainly didn’t find everything I would have liked in one place.)

I used a Sherwin Williams automotive high-fill primer. (This was my first experience with the product.) The body shop set me up with the two part primer and the thinner, all measured out and ready to go. I used my trusty HF 47016 spray gun. It’s a top loading, non-HVLP job that I’ve used exactly once before. Being a serious rookie, I read up ahead of time on how to adjust my gun. Here are some links that I found helpful:
http://www.sporttruck.com/techarticles/0609st_spray_gun_set_up/index.html
http://www.southernpolyurethanes.com/adjusting%20your%20gun.htm
http://www.stovebolt.com/techtips/hvlp_paintgun_basics.htm
http://www.purplesagetradingpost.com/sumner/techinfo/HVLPspraygun.html

Basically, the procedure seems to be to open all three controls up to maximum and supply the gun with maximum rated pressure. Then shoot a test pattern and adjust the material control and pressure to optimize the pattern. The only adjustment that I made was to turn the material flow back in ½ turn (3 turns out is maximum).

Everything seemed fine, but as soon as I started to spray, I noticed air bubbling up in the paint cup. I remember reading something about it but not what to do. Turning down the air pressure with the air micrometer on the gun reduced the problem to manageable levels, but also reduced the width of my pattern. Oh well, off I went.

I was able to go around the machine exactly four times before I ran out of paint. I only had to stop to fix the gun twice (various things kept coming unscrewed). My cartridge respirator apparently wasn’t quite what I needed, as I could really smell the stuff.

Here’s what I wound up with:

The primer certainly revealed problems that I couldn’t see before. The finish came out pretty well, a very fine orange peel texture. I don’t know if I could have adjusted the gun to eliminate that or if it’s just normal.

Next, I began sanding the primer smooth with 150 grit paper. This went fairly well, taking about 3 hours. The primer didn’t have much tendency to load up the paper. When it did, a few flicks with a wire brush would usually clear the paper. Here’s the result:

Sanding revealed more low areas. The next step was to fill the low spots and pin holes with spot filler. Again, I used Dave’s favorite: Evercoat Easy Sand. The Easy Sand is very nice to work with but the mixing instructions are bit off. They say to make a round pool of the filler and apply a ribbon of hardener that runs from one side to the other. I tried that and got a mix that hardened to rock in about 30 seconds and then got very hot. I was lucky to save my tools. I wound up using about 20 grams of filler with one drop of hardener to get a reasonable working time; it’s pretty easy to over catalyze.

The Easy Sand spreads much better than the Rage. I used a pair of HF shim steel spreaders to apply it. A low angle (say 20°) lays down a nice thin layer. You can then come back with a steeper angle, about 45°, and scrape off everything but the low spots. It doesn’t have the tendency to pull and tear that every other filler I’ve used has (to one degree or another). Sanding it, however, is another matter.

Sanding the primer on the base revealed a lot of low spots that I decided to fill with Easy Sand. Here’s where I’m at presently, with some of the Easy Sand sanded:

The same 150 grit, wet/dry Silicon Oxide paper that worked so well on the primer loads up almost instantly with the Easy Sand. I think they ought to call the stuff Easy Apply; sure goes on easy but isn’t sanding all that easily. I haven’t tried wet sanding yet, but I need to do something else. Maybe a different type of paper?

Cal

JRouche · Sep 4, 2008

Great job!!! The Rage Gold is the best plastic filler. Does help to knock off the big chunks when the are just starting to cure. A razor works really well to trim almost cured filler.. If you wanna get fancy and fill the pin holes before the HB primer I can recommend Evercoat's metal glaze. Its a spot putty. Use sparingly, a skim coat. JR
http://www.evercoat.com/productDetail.aspx?pID=184

Ooops. I posted right after your last post it seems

Great job.. Wanna come over and finish my 62 Nova I have been working on LOL

DaveE907 · Sep 5, 2008

Evercoat's Easy Sand and Metal Glaze are quite similar in mixing, application and performance however the Easy Sand cuts better with sandpaper. There could be two problems with your trouble sanding the Easy Sand. Properly cured and with the right paper it cuts very well.

First of all, sandpapers are not created equal. For this dry sanding operation the best product I've found is 3M Tri-M-ite Sandpaper. It's a non-loading dry sanding paper with open grit and is available in 150A grit. A wet-dry paper isn't what you want here, it will load up fast.

The second possible problem (and I hate to mention it) is under catalyzed material. In this case the material doesn't reach full cure and remains somewhat gummy. I've never mixed any of these products by weight so can't comment on it. The best description I can come up for a small amount of Easy Sand is for about one tablespoon of material use about the size of a small pea of hardener. Here's a photo I found of a batch of Easy Sand that was ready to mix.

Steve in SoCal · Sep 5, 2008

On all the products that use a catalyst, temperature has a big impact on how much to use and how long the work time is. In very hot climates it is best to use these in the early morning when it is coolest. In ambient temps over 90F with the correct ratio of catalyst, filler may start setting up in as little as 30-45 seconds. Using less to prolong the work time induces poor curing and gummy texture. You can use less by ratio in hot weather but you do have to be mindful of the trade off and use enough to ensure a full cure of the batch.

The same issue to a lesser extent affects the paint, are you storing the paint in a fridge? This will keep the paint fresh until you use it and unless it is in a cooler it will start to go bad quickly if mixed.

Steve

JRouche · Sep 5, 2008

DaveE907 said:
First of all, sandpapers are not created equal. For this dry sanding operation the best product I've found is 3M Tri-M-ite Sandpaper. It's a non-loading dry sanding paper with open grit and is available in 150A grit. A wet-dry paper isn't what you want here, it will load up fast.

The second possible problem (and I hate to mention it) is under catalyzed material. In this case the material doesn't reach full cure and remains somewhat gummy.

Exactly!! And I recently used some of the Tri-M-ite film in 220 grit while working on the car. That stuff doesnt load up much at all, and stays sharp for a long time. I like the 3M "gold" autobody paper too.

I love yer pic of the ratio for hardener. Believe it or not the directions are hard to gauge. They say a ribbon across the width or whatever. Its confusing. You show a good ratio, a lil HOT but I prefer hot to gummy.

Yer better off with a hot load that maybe you cant use all of instead of waiting a day, even two, or never, for it to cure..

Great pic!!!!! JR

Cal Haines · Sep 5, 2008

I'm sure you guys are right about under catalyzing the filler. I did a couple of batches that started to get cheesy at about five minutes and those areas sand much easier. The problem is that I wound up throwing away most of those batches. The last batch I made was used on the problem area and it was still soft after 10+ minutes. I'll give it a little more time to cure before I try sanding again. If it's still acting gummy, maybe I'll try a heat gun to try to speed it up. If that doesn't work, I guess I need to find a solvent that will take it off. Any suggestions?

The lathe is in an air conditioned space, but it's curtained off from the AC unit for dust control. It stays about 78 degrees (according to my IR thermometer). I've been mixing the filler in a small work room open to the outside. Outside temps are about 95 right now when I'm working.

Cal

archimedes · Sep 5, 2008

Cal,
nice efforts. its a huge undertaking to provide the rest of
us with words, pics & the patience to get it organized
for presentation. thanx.

PWP · Sep 5, 2008

Cal,

Be carefull with the two part high build primer. If you can smell it during spraying, this is a serious heath risk. DO NOT use again until you get the best respirator you can afford. This also includes any two part paints. You really should to be using an air supplied respirator.

Paul

JRouche · Sep 6, 2008

Cal Haines said:
If it's still acting gummy, maybe I'll try a heat gun to try to speed it up. If that doesn't work, I guess I need to find a solvent that will take it off. Any suggestions?

Yup, I have had a gummy batch, my fault. I tried some extra heat to cure, heat gun. No matter what, it was still soft. Fingernail test. If the nail was able to make a mark it was done. So I removed it with acetone. Works well on uncured polyester filler. Now I was worried cause I had some filler (cured and sanded) next to the stuff I wanted to remove. I didnt even want the whole thing turning to goo and have to REALLY start over. It didnt attack the cured stuff for what I could tell. I didnt wash it with acetone either, spray bottle and a clean rag. The uncured stuff came off pretty well. I checked the cured stuff and it was still hard. It will absorb though so give it plenty of time to dry out before placing new filler JR

DaveE907 · Sep 6, 2008

Lacquer thinner will also work to remove uncured polyester resin. If there is insufficient hardener the batch will never cure, it has to come off.

It sounds like temperature could very well be the problem Cal. Mixing the material in a hot area will warm it up and make it set up pronto. An area open to 95* F is far too hot! A good rule of thumb for chemical reactions is an 18* F rise in temperature will double the reaction rate. This reaction is exothermic and once it gets going and heats up the material you can't keep up with it.

Store the materials in a cool place.

A dodge I use to keep the mixed material cool in hot conditions is to use a cool piece of .38" to .50" aluminum or stainless steel plate as a mixing board. Mix the material and keep it spread fairly thin, .10" or less, on the plate to keep it cooled down. Cool the plate in water at a temperature that won't cause condensation on the plate in your relative humidity conditions, dry it completely and mix the material. Around here I shoot for around 60* F.

About the Surform versus rasp: there's no comparison. A rasp acts as a multiple tipped plow and digs grooves into the surface that you then need to fill or sand down. A Surform acts more like a multiple edged plane and leaves a far less damaged surface to work. It will also remove material at a prodigious rate. Use it when the filler can still be dented with your thumbnail and the initial shaping goes really fast, in seconds really.

Cal Haines · Sep 6, 2008

Hi Paul,

Thanks for the word of caution on the two-part primer. I don't plan to use any more of that primer and I will definitely be getting a better respirator. Any suggestions for a source?

Dave & JR,

The Easy Sand has had almost 3 days to cure and I can still mark it with my fingernail, so I guess it's not going to set up. I'll try the solvents you suggested and pick up some different sand paper.

I didn't have nearly as much trouble with the Rage as far as catalyzing goes.

I think I was wasting my time trying to fill the low spots on the base in the first place. The surface was much smoother before the primer. I suspect that the primer didn't go on evenly and sagged a bit on the vertical surfaces. I think I'll try a bit more aggressive sanding once I get the Easy Sand off.

Cal

9100 · Sep 6, 2008

Respirators

I use North respirators, sold by WW Grainger. The thing I like about them is the wide range of filters available, allowing you to match the material. I have some with activated charcoal. I can stick my head down in my vapor degreaser ( not turned on ) without smelling a trace of perchloroethylene. I agree, though, that one fed outside air would be better.

Bill

Cal Haines · Sep 20, 2008

The under-catalyzed Easy Sand never set up. I tried both acetone and lacquer thinner to remove it. The acetone seemed to work a little better, but neither one was taking it off very quickly.

I picked up some of the 3M Tri-M-ite paper in 150 grit. The only place I found that stocked it only carried 25 sheet packs. (I now have a lifetimes supply.) I also bought some 3M Sand Blaster 100 grit paper. I wound up using the Sand Blaster paper to sand away the under-catalyzed Easy Sand. The Sand Blaster seems to work about as well as the Tri-M-ite and is easier to get.

As I had surmised earlier, I was trying to fill low spots that I didn’t need to fill. I’m pretty sure that the air bubbling up in the paint cup was causing the gun to sputter and lay down an uneven coat of the high build primer. The problem mostly showed up when I tipped the gun down for working on the base. (I think this was caused by not having the tip/cap of the gun tight enough.) Anyway, I was able to sand down the high spots in the primer on the base. The headstock and gearbox didn’t have too many issues.

I’ve been painting some of the parts a darker grey for a bit of accent. Things like the wiper covers, handles, the vertical trim strips on the covers, etc. Here I’ve masked to paint the front spindle bearing retainer the darker grey:

I’m putting topcoat on the retainer first because it’s a lot easier to mask it off for final coat on the headstock than the other way around. Here’s the headstock after painting the retainer:

I wish I had painted the whole machine the darker grey. It’s a lot closer to the original color.

I was planning to sand the retainer with 400 grit and put a final coat on, but it turned out “good enough”. (SHMBO keeps reminding me that I’m not restoring a Stradivarius.)

I’ve given up on the Easy Sand for filling in pinholes and such. The Bondo 907 filler is a lot easier to work with and clean up. You can see where I used Easy Sand to fix a low spot on the left side of the headstock, over the front spindle bearing. I guess I got a bit too enthusiastic with the sandpaper-wrapped dowel as I was trying to blend the 90 radius with the top of the headstock. I made a wooden block with a matching radius on the end and carefully block sanded the filler to match. We’ll see how well I did when I get the topcoat on.

Earlier on I had decided that the base was “good enough” and had concentrated on the headstock and gearbox. I guess now that I have a little more experience, I see things that I didn’t before. I finally set up some decent lighting and got some padding to sit on so I could do a proper job of sanding the front of the base. I only have 12 inches between the back of the lathe and the wall, so I wasn’t able to work quite as effectively there. But on the bright side, there isn’t much room for critics to find the holidays either. I probably spent about 6 hours resanding the base. I wish I had done this before the high-build primer, as I probably sanded about half of it off.

Here the back side of the base is almost ready for top coat. I just need to finish sanding the Bondo 907 flush and clean up the space for spraying:

The next step it topcoat! I don’t a darn thing about thinning paint to spray. I bought a viscosity cup, with a 4.0mm orifice; DIN #4. My gun doesn’t specify the viscosity that I should thin to. Any suggestions? My gun has a 1.4mm nozzle, if that helps.

Thanks for all the suggestions and encouragement!

Cal

PWP · Sep 21, 2008

I have been painting for 30+ years and never have used a viscosity cup. I planned on buying one years ago, just never have! I judge how thin the paint is by how it drips off the stir stick. Certainly not the best way. I tend to start with less thinner/reducer shoot a few test patterns and look for orange peel. Add thinner if needed. I have used SATA HVLP gravity feed guns forever. If the paint it is too thin and your gun speed is too slow, you will get runs. A 1.4mm tip should be fine. Take your time, keep the gun moving, and parallel to the surface. I would suggest that before you shoot the topcoat, that you shoot a good quality Primer/Sealer. Again, make sure you wear a proper fitting respirator with proper filters. Also, It's a good idea to cover up any exposed skin.

Paul

Cal Haines · Oct 10, 2021

Before:

After:

Cal

220swift · Oct 10, 2021

Very nice looking paint job.

Hal

paint prep - part 2

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