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Are those mile long sanding blocks a gimmick?

22K views 43 replies 22 participants last post by  35WINDOW 
#1 · (Edited)
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.

Brian
 
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#2 ·
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.

 
#3 ·
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.

Brian
 
#4 ·
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.
 
#5 ·
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"
 
#6 ·
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.

Aaron
 
#7 · (Edited)
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
 
#8 ·
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.
 
#9 ·
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...
 
#10 ·
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.
 
#11 ·
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.
 
#12 ·
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.
 
#13 ·
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.

Aaron
 
#14 ·
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
 
#15 ·
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:
 
#19 ·
How can they be effective ??

As most of you guys know from the very basic questions that I've asked and some of the "problem areas" you have helped me thru, I'm a rank amateur when it comes to body work.

I looked at some of the very long blocks with an idea that they might help me finish the car that I have been working on forever. First of all, when I grabbed hold of one, a 24", it felt wrong - that it was not controlable. Any flex that wasn't under my hands could not conform to a rounded panel, that anything longer than a 10 1/2" Durablock which my hands cover wouldn't work right for me. While I do have a 17" rigid long board that I used on the door and trunk, it feels "in control" because it does not flex. If it were possible, some pressure probe pickups would confirm that wherever your hands were, would have higher pressure and would tend to cut lower areas, and any area between them would tend to make a flat - both usually exactly where you don't want them. The idea is great, but the physics are wrong(at least for my untrained hands). :D

Dave
 
#20 · (Edited)
Hey now, we've got a 30 inch long block at the shop. It has a pretty thick sheet of stainless steel for a face. So, it's flexible, but not real flexible. And, I've used it with lots of success. It really is a matter of blocking technique (lots of steady even cross-blocking). Maybe not the tool for the average guy, but, great if you have to skiff a whole roof. :thumbup:
 
#21 ·
The 32inch board I use isn't flexible (oak handle with alluminum plate), works great on long flat panels and I sometimes use it on low crowned areas like roofs but the contact area is smaller. The rigid boards are for shaping and the flexible blocks I use for finer grits after the shaping has been done. Works for me...
 
#22 ·
The Long and the Short of sanding

My collectiond of sanding blocks stems from the trditional paint stick to my new 21" longboard (I sent the 36" back because it was too clumsy to use). I have found that whatever method you prefer in sanding, it's always best to use the longest board possible. This doesn't mean to use a 4' board because your roof is 5' long. The longest board you feel comfortable with that still allows for straight even pressure strokes is where I like it. I agree with all who like the 17". Sticky back paper is readily available and the length seems to suit me for most of my needs. My 21" requires that I buy 3M Gold 45yd rolls. somewhat of a cost savings and no leftover paper to throw away. The adjustability of this longboard is sweet when it comes to initial sanding.

In my favorite of restoration (Old Trucks), the 21" is about as long as I can go due to the rounded bodylines of yesteryear. About the only place that I really see a primary use for this length is on the hoods and roof. The 17" and smaller covering everything else. I will tell you that one project I found that would require 21" or longer board is a 27' foot boat that I had the pleasure of repainting. Since most of the surface was flat and highly streamlined, the "longer the board the better".
 
#23 ·
The area where I have seen long boards used to good effect was on boat hulls -- long (30 feet) continuous curves. And the really fussy guys do get somewhat better results with them, but to tell you the truth I have seen other people do just as well not using anything longer than 18 inches. I think it is more a matter of preference. The fussiest guy in my area swears by them, but the guy I prefer to use when I have work done does not use them and gets as good a result.
 
#24 ·
Flexblock?

jcclark said:
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:
Where can a flexblock be found? What brand & maybe part number? Thanks
 
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