Grinding Disc?

General Discussion
1

I’ve been learning surfboard reapair over the last few months.  I only have a sander/polisher and a Medium Flexpad with various grits of sandpaper.  Good for most things, but I’m looking for an attachment that “digs” into the board more rather than sands flatly.  Something that, for example, I can use to clear away broken areas and take off targeted, deeper sections of fiberglass.  Something that can be used at more of an angle (angling my Flexpad too much just rips the paper off the edges) or even completely on it’s side.

Am I making sense?  LOL  I notice some repair/shaper guys on YouTube using a thinner, plastic-looking disc in the manner I just described.  What exactly am I looking for?  And what is a good brand to get?  

 

Thanks!

2

Maybe a right angle die grinder and a 2 or 3 inch 3M Roloc disk??

3

Ohhhhhkkkayyyyy, a few things-

Depending on what you have now as a ‘sander-polisher’ you have a few options.

But first, you really don’t want to be grinding away a whole lot. Trust me on this one, you suddenly discover you have made a simple easy job into a gaping crater. Been there, fuc#ed that up, the less you rip out the better. 

Meanwhile, back at your sander-polisher. If it’s an orbital/random orbital type, especially a palm type, it won’t take a grinding disc, the way to get more off faster is with a coarser paper. 

If we are talking about a 7" or 9" sander/grinder/polisher like the 12-15 amp Milwaukees or to a lesser extent the Harbor Freight versions ( lower amperage) - bear in mind that grinding wheel/grinding disc setups like you describe on those are for grinding fairly heavy steel or thick fiberglass or heavy wood. Welders love 'em. Guys who grind thick paint off work boat hulls use them. But by comparison, a surfboard is an eggshell.You can destroy it real easy with a coarse grinding disc. 

Smaller disc grinders are lovely tools…for grinding metal or thick solid glass, or getting rust and paint and smeg off metal with a wire brush rig. I like mine, for that. I have seen wheels for those with a rim that’s chainsaw chain, used sidewise as you describe, for wood sculpting. But with any disc in a disc grinder, those things turn hellaciously fast, not a ding repair tool. 

The experienced professional guys who sand hotcoats and polish gloss coats are using sandpaper discs and medium-soft foam backing discs and using them carefully, pretty flat. You use firmer foam backing discs for things like boat hulls, made of solid thick metal, glass or wood. Note that I say experienced - it’s real easy to make bad things happen. Guess how I know…

Now, I have no idea what you saw on Youtube. But you want to bear in mind all the other stuff you’ll see there, the ones that start with Hey Bubba, watch this. Those don’t turn out too well. 

hope that’s of use

doc…

 

4

I use a small pneumatic die grinder with a sanding disc. Pretty easy to control, but you still have to be very careful. 

5

I have an actual Makita sander/polisher.  Forgot the Model, but I’ve seen it mentioned on forums like this.

One video I remember was Joe Roper.  I would guess he’s “legit.”  He used a thinner and hard-looking disc in his sander/polisher to do the initial rough work.  Then he had a softer pad in a later clip.

6

Take a look at our 2" Fiberglass Sanding Disc Holder for Power Drills.

 www.greenlightsurfsupply.com

 

7

Ohhhkaaay, that’s this video?

A few things- 

First off, he’s doing it right, start to finish. **Minimal **rip rend and tear, preserving as much of the original as possible, then adding plenty glass, minimal filler. Adding white pigment to the filler, by the way, excellent idea.  The way he’s using a tongue depressor to force the filler in, bridge the depression and leave something faintly concave, sweet. 

Mr Roper has been doing this for decades and it shows, He’s really, really good at it. His sander technique is excellent. Note that he’s holding the disc as flat as possible whenever he can, very very light pressure, just a touch with the outside of the disc ( not the edge)  when he’s looking to get into a divot. This is the sign of a lot of experience…and having made mistakes in the past.  He’s not doing initial rough work, he’s doing very careful prep work, and there is a difference. 

The first disc he uses ( up to about 2 minutes into it) appears to be a firm-ish foam pad backing disc, adapted to the very healthy sander/grinder ( Hitachi/Metabo I suspect) , looks to be a 5 or 6" that uses stick on paper. Nice rig. The yellow foam is typical of 3M products: see 3M backing discs here I couldn’t tell you if he’s using the ‘hookit’ ( velcro-like) or ‘stickit’ (peel and stick) discs on the thing. There’s something to be said for both. Wide variety of grits and construction/composition available, also from 3M, your friendly neighborhood auto body supply is a good place to look, or Grainger or similar.

I’ll note that, perversely, I found the smaller discs harder to control than the big ones doing boat work and dings. Might be just me. .  

The bigger disc, yep, softer pad, bigger diameter, probably also 3M, same thing with the discs and sources… 

Now-  you say

I’ve been learning surfboard reapair over the last few months

See, there’s the thing. I’m not gonna discourage you from that, it’s a good skill to have and once you get good, and fast, and efficient, you can make some money at it. I did. In my so-called ‘retirement’ I may have another shot at it. 

As Mr. Roper says towards the end of said video, “If you’re not 100% skilled” - you maybe want to hold off a bit before you go attacking boards with ferocious industrial tools.He probably has forty years in with heavy sander/grinders.  They’re a wonderful time saver in doing very large ding repairs like buckles and busted boards. I found that the time I saved paid for the tool. But that was after a long time in. And having spent my youth in a boat yard with heavy grinders and being taught how to use 'em precisely. 

I’d suggest that you hold off on the bigger sanders for the moment, Practice on junked boards. If you can find somebody like Joe Roper to work for for a while, that would be ideal.

hope that’s of use

doc…

8

Wow, thanks Doc.  Nice post.  Really helpful.

That was one of the videos.  Another one, I think with Roper’s son, initially used a black disc thing in similar fashion.

I’ve mostly been working on junk boards that were given to me or just abandoned at my local break’s parking lot.  I’ve only recently started working on my “real” boards, and that’s been  all by hand.  I really like messing with the machine though (except for all the mess) so I’m whipping it out on my good boards sometime in the not-too-distant future.

9

Ah? Good, I hoped you wouldn’t take it wrong like I was talking down to you, we all started out and worked our way up. 

Now, let me suggest a middle ground?  The Porter Cable 7335 5" variable speed random orbital sander or the very similar 6" 7336, the only difference is the 5"or 6" sanding pad itself. Built on the guts of a smaller disc grinder, the side handle makes it very controllable. P-C discontinued it some time ago but you can find them used and cheap, craigslist, FB marketplace, used tool stores. You should be able to find a really good one for $50.  And with the right paper on 'em, they can take off a lot of material pretty quickly, with finer paper you can get it to where all that’s needed after is wet sanding and polishing. 

Industrial built ( probably why they were discontinued ) , about the only thing that wears out is the brushes and pads which are easy to replace. As a bonus, the techniques you pick up using one of these are a direct lead-in to the bigger grinder/sanders, how you handle them sanding flat or with a little of the edge is pretty much how you handle and work the big suckers. It transfers well.

The other nice thing about them is you can do good, fast work on smaller dings, shatters and what have you that the big sanders are just way overkill for. Great tool for bumping up your production rate.

Mine have the peel and stick type pads, keep them clean ( a wipe with acetone now an again) and dust free so the damn sandpaper discs don’t go flying off, Change discs when they get a little dull or clogged, friction heat softens/weakens the adhesive so they get loose on you. I am told they have velcro-type retrofit pads, the discs cost more but are more easily switched out and are usable again after you switch them. The peel and stick are one-shots.

There’s a variation with holes in the pad and the discs and a vacuum attachment. Myself, I think those are just awkward, the hose and all is a pain and you should be wearing a good dust/organic vapor mask when doing dings anyhow. That’s me, your mileage may vary. 

There’s a similar Milwaukee, probably a good tool, I looked at them when they discontinued the P-C. There are also a lot of palm type one handed random orbital sanders that are just not controllable to the extent this type is, not recommended. 

hope that’s of use

doc…

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10

Brian @ Greenlight and McDing have the right idea.  At least it’s the way I do it.  Plug one of those Rol-Lok discs in to a 3/8" electric angle/‘close quarters’ drill and you will be able to tackle a bunch of sanding/fixing jobs.

Bigger softer pads are the rule for full board sanding but for hogging out (gentle prepping) damaged areas, I like those ROL-Loks in about a 60 grit.  

 

 

11

Disks and, sanding pads, “hook and loop"sandpaper etc can all be bought to use on the sander/polisher that you already have.  A variable speed sander/polisher by Makita, Milwaukee is standard for anyone doing ding repair.  Just do as Joe does and you’ll be fine.  Flex pad sells paper and disks on their website.  So does FoamEZ, Fiberglass Hawaii and Surf Source.  Indasa and 3M.  I have used 9x11” sandpaper on a Flexpad attached with spray adhesive as long as I can remember to sand hot coats and do ding repair.  Learn to use it properly and at the right RPMs.   Orbitals are usable, but not optimal.   Much more variety in pads and paper for a sander/polisher…  No one working with fiberglass should be without a Sander/polisher and a Die Grinder.  Inexspensive versions of both can Be bought at Harbor Freight.  3M Roloc disks can be bought online.

12

I have one of these and like it very much.  But the only thing I use it for is to get rid of swirls at the end of a hotcoat or Wet&Dry sand.  Pads have to be custom made and put on with spray adhesive if you want anything softer than the pad that comes with it.  Otherwise very usable for flats.  Dewalt makes a nice one as well that comes with a dust shroud…  Have used the Makita 5" for years as well.  But almost never for surfboards.

13

Umm, when I was looking at the 3M backing pads…well, as my old man used to say, “A dullard is someone who can go to an encyclopedia and only look up one thing”  so I got sidetracked. 

And here’s the thing - the pad on the 7335 is a cute little unit which mounts using a threaded stud that’s attached to it. As it turns out, that’s the generic way of making a random orbital sander pad. 5/16"x 24 thread is the standard. I have not checked my pad, but…  

And it turns out 3M makes a bunch of them for random orbital sanders. 3M must have a tech writing department, there’s a lot of documentation out there. Made.in varying diameters, thicknesses, hookit ( velcro) or stickit (stick on), hard, meduim and soft,  and with or without holes in a number of patterns. If you don’t like what 3M has,  they’re kinda generic, lot of other makers, many cheaper by far than the original P-C part. 

hope that’s of use

doc…