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MARTINSR 09-04-2006 08:55 AM

Are those mile long sanding blocks a gimmick?
This is a portion of a post of mine that I posted in discussion about these super long blocks on another forum. (click here for the thread at Team Chevelle) These are my thoughts on these monster blocks, am I off base, do they really make a difference? The answer from Durablock on the original posters questions about wrinkling paper was particularly interesting and seems to support me.

I don't use anything any longer than a 17" "Long board". This is how I see it, and yes I can get a car VERY straight, if the long board is ran across that door it is going to flatten it just as good as a 30" block. I mean, if there is a low spot in the door that is wider than the 17" than you have other problems, more serious problems that no long block is going to fix.

Let me put it this way, those super long blocks have only been around, what maybe ten or fifteen years? When I first started in this business there was no paper to even go on these long blocks, they simply didn't exist. So were there no straight cars? Of course not, there were cars just as straight as now.

The thing is, NO Panel is "flat", none, period. So, what good is a block that when laid on the panel is up off panel at each end? Honestly, how could that block that is not touching more than a foot or two at a time block the panel any straighter than a block that was that foot or two? It can't, that is the fact.

The curveable blocks don't CUT the shape because it doesn't match the shape either. I mean, it will match a PORTION of the panel, but again, not the whole thing. So if you bend it into shape it will only be good over a small area. And if it flexes to fit the shape, it won't be "flat" enough to CUT the high spot "flat", I just don't get it. I have tried them, I have used everything you could imagine at one time or another to shape things. When it comes to concaves, I have used rolls of paper towels with paper on them, every friggen size rad and heater hose you can get. I have bought wood blocks cut to the shape of body lines, half round "blocks" and so on. But with "flat" panels, good old rubber blocks, long and short and long boards are pretty hard to beat.

Durablock round, and the long rectangular ones are super and I use them. But the super long monsters, I just never found a need. I may be working on a car in the future where I run out and get one because I decide on that project I need a super long block and really like it, I don't know. But as of now, I have lived without it.


Rambo_The_Dog 09-04-2006 10:04 AM

Great post - I've been wondering the same thing recently - hopefully you'll see some good feedback from folks who use these style blocks

I have a similar background - never using anything more than a 17" block through my 35+ years doing this stuff. I also feel the same way that in if you have a low spot that's over 17" you have a big problem!

Personally I feel most people problem with getting panels straight is not letting the block and paper do the work - ie. applying excessive pressure while blocking causing the panel to move...

However, I have a 49 Hudson Commodore that has a HUGE rounded roof and I was thinking one of the longer flexible blocks would be expensive :pain: yet perfect for shaping and blocking this area.

MARTINSR 09-04-2006 10:14 AM

This is one of the points I made Rambo, how would one of these flexable blocks work when it is, well, flexable? I mean, why not glue the paper to an old bike innertube, it's flexable as well?

That is my point, how can a flexable "block" be a "block" at all? Isn't the point to use something that DOESN'T follow the highs and lows? The point of a block is to BLOCK the highs down to the lows isn't it?

If the block is "firmly" flexed into a position then what shape is it in? The shape of that roof changes a zillion times as you pass over it. So how can a "shaped" block sand it flat when it only it's shape only matches the roof's shape at one particular point?

Like I said, I tried them, the old long board that was plastic so you could curve it to the shape of a fender and it just didn't work and didn't make any sense at all to me.

I block curved panels with a hard block and simply look at at it as a "curved flat" panel. Just taking a bite sized piece at a time until it is all done.


oldred 09-04-2006 10:31 AM

I have a 24" and a 30" block and so far I have found little use for the darn things. I tried the 24 a few times and it is ok I guess but the 30" just seems to do more harm than good, for me anyway. I thought that it was just that I needed to learn to use them but after reading this I am thinking maybe it is not me after all.

BondoKing 09-04-2006 10:31 AM

Interesting post Brian.. I have wondered about this, it is the reason I was asking about the PSA paper vs. Velcro.. I have a 24" durablock I cant keep the paper in the center held down since it bows to match the curve of the roof lines.. which does make it more difficult to not have a high spot right in the center of the roof, so I ditched it and went back to my 12" durablock I think.. dont have a 17"

adtkart 09-04-2006 10:32 AM

I have said before that no panel is made to be perfectly straight. The large corves in that roof panel are an area that the LONG block may help with. The idea of those long blocks is that they make the curves more uniform and gradual. Since they are in fact flexable, you would need about 10 hands to hold pressure on the whole block while moving it. You could, however, on a large curved panel, place one hand in the area of each end, and cause the block to bend to match the general curve of the panel. That way, you would be removing some of the slightest "steps", that you can get from sanding many different areas of those curves, and try to blend them together.

That being said, I am still not going to run out and buy one. The "steps" that I mentioned, when the work is done by someone that knows what they are doing, would not be noticeable by eye. If you made an exact set of templates, you would likely be able to see a difference across the panel. Then again, you cannot get it perfect anyway, without a set of templates, and working yourself to death. Not worth all of that to me.


powerrodsmike 09-04-2006 10:35 AM

Keep in mind that I am not a "bodyman" who does alot of steel car blocking, but I do tooling and modelmaking for fiberglass.

I have a 4' long by 6" wide sanding board that I made. Semi flexible. I use sandpaper from a belt sander. (cloth backed resin bond sandpaper lasts forever when using it by hand) I glue the paper on with feathering disc adhesive so it doesn't wrinkle..
I make board the conform to the curve by pulling the handles together. It does require some "feel" to work it correctly.

I have found it to be indispensable when I am doing tooling for roofs, and tonneau covers and large, one off custom panels. I would not have been able to make the streamliner body in my photo album as straight as I did, (faired to .040" in 4',before priming it with 40 mil of sanding primer), without it. It is a fairly exertive activity to push that board all day. :sweat:
I do use it for the shaping all the way down to 80 grit, then I switch to my shorter boards.

I personally would be lost without my 17" flexible, my 17"rigid or any of the other shaping boards that I have or have made.
The older pre war stuff with fairly severe compound curves are really hard to get wave free without the flexible ones..(for me anyway)

I did some consulting a few years back to a boat builder in the carribean islands, (yes ,someone paid me to help them), where I saw guys using "gang boards" 12' long and 6 inches wide. They were semi flexible.4 to 6 men would work together sanding fair these 65' catamaran boat hulls. (you gots to have rhythm, mang) There is paper available for those boards. Boat shops carry it.

The "wave sanding theory" I learned says: In fairing large objects you want a board that is as long as 2 times the distance between the longest wave you are trying to sand out.

It makes sense to me. But that's just me. :P

I would say that long boards have their place. :D

later, mikey

jimk 09-04-2006 01:32 PM

They work.They have ones with rods in it to keep the shape the same.They have flexible ones.They all work great.I just did a 1975 Caddy Eldorado.Came out straighter than most other cars I have ever seen.I usually only use them on real long cars.The flexible ones are not as flexible as you think.It has a little stiffness to it.

crashtech 09-04-2006 08:00 PM

I guess it all depends on what you are working on. For every auto I have ever done, the 17" block has been plenty good.

For waves that may be larger than that, a flexible aluminum yardstick kept in good condition will reveal problems quite well. They can be placed perpendicular to a flat panel or layed down on a curved one. With a bit of learning and technique, a critical eye and decent light, large size waves can be detected and the high areas worked down by carefully concentrating sanding in that area, and rechecking often.

I've even been known to rub the yardstick against primer or filler, a bit of the aluminum will rub off and mark the high area, though of course this puts wear on the yardstick over time...

beemdubya 09-04-2006 08:33 PM

I have a 17" duablock.. i couldnt see using a longer durablock then that.. what i found works really well is 1/4 plexiglass cut to almost any size.. Plexiglass is still very rigid but also conforms to most curves. Ive used this method on a few cars now one being a black 66 gto(which is basically a flatter bodied car for the most part) and one being a 1993 mazda rx7 (which is basically a huge round bubble.. curve) both cars are extrmely straight.

I feel that you sometimes need some flexibility.. but a huge long flexible block could prolly do more harm then good and really hard to control.

shine 09-05-2006 08:30 AM

when i started we were working on a lot of early 60's stuff. EVERYTHING then was 20ft long and flat. try blocking the 63 chevy qrt panel. things as long as a vette. i made my own blocks from soft wood and glued paper to them. had on that 3 sheets long. great for blocking bodywork on one of those qrt's. they do have their place. i still use all of them from time to time.

rt428 10-04-2006 09:38 PM

I don't have a fraction of the experience some of you guys have. From a novices point of view, I found that anything longer than my 17" Durablock would be very difficult to control for larger panels. I liked using both hands about 1/3rd of the way in from each end and "controlling" the arc with my wrists. I was able to do a better job with my body work which made blocking my first primer coat easy to with just a 12" "skinny" durablock.

adtkart 10-05-2006 04:55 AM

rt428.... Just keep in mind that the cutting is not done by pressure on the block. It is the paper itself that does the cutting. The pressure on the block should just be enough to hold it against the panel. With the flexable blocks particularly, the amount of pressure will have a big effect on the contour of the panel. With the longer flexable blocks, you can end up with it cutting low spots where your hands are, while you are trying to cut what appear to be high spots in the middle. They take practice and concentration.


BondoKing 10-05-2006 06:43 AM

Practice pratice is what I am saying these days, with whatever one you are using.. Just as the old guys got used to using possibly shorter blocks on longer cars.. todays guys are possibly using longer blocks on shorter cars.. go figure..

I used a 24" Durablock on the roof of the Mach 1, and after talking to Aaron went back over it with a 11" one I dont have a 17" one, anyways and completely reblocked it..I had one slight wave dead in the center that was not going away and I did not feel it until I started sanding with 320.. go figure.. the rest of the roof felt perfect and rounded etc.. , so after a long evening of blocking and the unfortunate "bringing out of the hammer and dolly" again, I got it..

Im taking my 24" Durablock to JCCLARK and let him put it on one of his saws and whack it down to 18"... You need 3 hands to hold that longer board properly over a really long surface.. at least this is my findings so far

jcclark 10-05-2006 08:47 AM

My longest block is 17", I rarely use it though, most times my smaller
ones do just fine.
I recently tried a new block I really like for curved panels. It's
called "Flexblock" and is just like my other foam blocks but has slots
cut in the top that allow it to flex and follow the contours.
This has really helped my curved surfaces get more consistent. :pimp:

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