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How do deal with compounding errors

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Forum topic by Vududude posted 07-12-2013 07:01 PM 793 views 0 times favorited 15 replies Add to Favorites Watch
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Vududude

41 posts in 443 days


07-12-2013 07:01 PM

So, new to woodworking, had successfully completed a pretty simple stepping stool. For my 2nd project I wanted to build a diaper changing table since we’re expecting our 2nd child soon. It’s a simple design…http://www.landofnod.com/baby-changers/kids-furniture/1

The problem I ran into is that I did all the calculations, cut all the pieces to length. But what I’m guessing is that small little inconsistencies in joinery, crosscutting, length have led to small, but noticeable imperfections.

For instance, I decided to have the legs be 2×2s, with the stretchers flush to the sides, so this meant I had to notch out the corners of the MDF shelves. Put those all together and it turns out that my stretchers are now 1/8 of an inch to short, either because my stretcher weren’t exactly flush with the sides of the legs, wood movement, MDF swelling or my own error.

So I guess I wanted to ask how do you typically deal with these issues? I tried to cut all the pieces as exactly as I could, but once a small error is introduced, it just seems to magnify and I’m left with needing to cut new stretchers to make sure it’s a good joint.

thanks for any advice!


15 replies so far

View firefighterontheside's profile

firefighterontheside

4271 posts in 508 days


#1 posted 07-12-2013 07:17 PM

Well, I have been known to make the whole rest of something shorter to account for the fact of cutting one piece too short. I have also drilled holes in the wrong place and so just drilled a larger hole and used a plug. To make it uniform, do the same thing in corresponding areas to make it look like you did it on purpose. If you are dealing with MDF its not too expensive so the best thing to do is probably just make new piece. The more you do this, the better you will get at measuring. Make sure you have a tape that is not causing problems. The ends of tapes can get bent when you drop them. They will still measure correctly when you are butting it into a corner, but when you hook an end it will cause you to make things shorter than intended. I bought a little 15’ tape to use for woodworking, but it turned out that after I hooked the end, the tape hook would slide up a bit and make my measurements off by a little bit. This is only your second project. Don’t be too hard on yourself.

-- Bill M. I love my job as a firefighter, but nothing gives me the satisfaction of running my hand over a project that I have built and just finished sanding.

View BTimmons's profile

BTimmons

2123 posts in 1137 days


#2 posted 07-12-2013 07:26 PM

Do you measure all your pieces, or do you gauge them? That’s an important distinction, and one that might not be that intuitive at first.

Say you need to cut four table legs to length. Call it 30 inches. Given that task, most people will get out the tape measure and mark each piece at 30 inches. The problem arises because each time you measure, chances are that you’re just a little bit off the mark compared to your last measurement.

So here’s what you do. Measure one leg only and cut it to length. Now take the freshly cut leg and lay it atop the next. Make sure the edges are flush and square to each other on one side, use the edge of the top piece as a fence for a marking knife. Scribe the difference to indicate where the next piece should be cut. Repeat until you have all four legs cut to length. They might not even be 30 inches exactly, but this method will remove any inconsistency in the size of your parts.

Pencil lines can only be so sharp. Knife lines on the other hand, create an almost singular reference point.

-- Brian Timmons - http://www.BigTWoodworks.com

View rfusca's profile

rfusca

155 posts in 495 days


#3 posted 07-12-2013 08:13 PM

Describe your process and tools for measuring, marking and cutting. It doesn’t sound like it when you start out, but just measuring and marking accurately can be some of the biggest challenges. Getting two pieces exactly the same can be difficult.

-- Chris S., North Atlanta, GA - woodworker,DBA, cook, photographer

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Straightbowed

717 posts in 950 days


#4 posted 07-12-2013 08:19 PM

when I build something I measure one pc then cut everything by that pc or make a stop on my saw and just cut ething the same never measureing but one pc when I drill something I drill it stacked so every hole is the same sometimes I don’t measure just start cutting ething the same lenght and go from there do it by eye

-- Stevo, work in tha city woodshop in the country

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Straightbowed

717 posts in 950 days


#5 posted 07-12-2013 08:20 PM

good call Timmons thats the way I go

-- Stevo, work in tha city woodshop in the country

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Straightbowed

717 posts in 950 days


#6 posted 07-12-2013 08:22 PM

or most time I cut and finish with handplanes or the right handtool for a good fit

-- Stevo, work in tha city woodshop in the country

View ajosephg's profile

ajosephg

1852 posts in 2213 days


#7 posted 07-12-2013 09:46 PM

I never cut ALL of the pieces to a theoretical length to start with. Rather cut them all a little long, then cut them to fit as you go through the project, if you get what I mean. Also do what Brian and Stevo do.

-- Joe

View Loren's profile

Loren

7545 posts in 2299 days


#8 posted 07-12-2013 10:03 PM

Work to “relative accuracy” meaning the parts are accurate
in relation to one another. This differs from absolute accuracy
where parts are made to measured tolerances.

Absolute accuracy is a difficult standard to work to with
wood… working to relative accuracy using story sticks,
marking gauges and other simple devices is easier
in the small shop and when you get used to it
helps prevent mistakes.

Sometimes with angles you have to get pretty close to
“nuts on” in order to produce a good result though.

-- http://lawoodworking.com

View cutmantom's profile

cutmantom

282 posts in 1687 days


#9 posted 07-12-2013 10:23 PM

some parts are best determined after some assembly or dry fit, if some parts length is determined by more than one other part then you need to measure them when put together not go by the math, I think there is even a method out there somewhere that uses no ruler at all

View rhett's profile

rhett

699 posts in 2319 days


#10 posted 07-13-2013 12:29 AM

My only advice is, do not get discouraged by your mistakes. Making mistakes and seeking assistance, is part of expanding as a woodworker.

“A person who never made a mistake, never tried anything new.”
Einstein

-- It's only wood.

View JAAune's profile

JAAune

796 posts in 968 days


#11 posted 07-13-2013 04:11 AM

Unless you’re working with precision equipment (and you aren’t since you aren’t in a machine shop) you need to decide ahead of time where you’re going to put the error. It’s sort of hard to explain but I’ll do my best.

Right now I’m building some pews with arms that require 4 parts for each assembly which are then veneered. Between the various angles, two grooves and a rabbet it’s very easy to get variation from one arm to the next when building batches. What I’ve done is to decide which faces would be my reference points and every machine setup and jig uses those reference points. Because of this, any deviations caused by imperfect cuts will creep into some unimportant place. One arm might stick out 1/64” more in the front than the other but that harms nothing. Even an 1/8” would do little harm. All the joints are exactly where they should be.

Be careful about pre-cutting all parts too. Even though I work from highly detailed plans with perfect measurements included, I never cut everything to dimension up front. Instead, I usually begin with the most critical portion of the project then cut the remaining parts only after I can verify measurements. Often I’ll hold up pieces in place then mark the length with a knife.

Another useful trick for some projects is to build from the center out. All parts are cut and measured based upon a distance from a common center line.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View MT_Stringer's profile

MT_Stringer

1881 posts in 1883 days


#12 posted 07-13-2013 05:01 AM

I just finished building my 10th cooler. It is without a doubt the best one I have built. The difference with this build is it is the first time I have used my new miter saw and the new miter saw station that I have installed the Kreg precision measuring trak, I was able to make consistent identical cuts…like 30 of one length, 10 of another and so on.

Some of the boards I precut to the desired length because the measurements are set in stone and the same every time. Others were cut to rough length. As I got ready to install those boards, I measured and cut to fit.

Oh, by the way, I made a mistake or two and had to cut several boards again. Luckily I had extra boards for the next cooler.

Good luck. Keep on plugging away.

-- Handcrafted by Mike Henderson - Channelview, Texas

View Vududude's profile

Vududude

41 posts in 443 days


#13 posted 07-13-2013 05:35 AM

Thanks for all the advice.

I do end up measuring all my pieces individually, I didn’t even think to use the prior piece as a template for the next.

I think it’s mostly frustrating when a piece ends up being too short, since there it either means cutting another piece, or leaving a gap.

I really like the advice of not cutting everything up front…which is what I did on this project and I definitely regret that now.

I’m definitely learning a lot from these mistakes, and from all the advice from this site, I really appreciate it!

View reedwood's profile

reedwood

880 posts in 1328 days


#14 posted 07-13-2013 01:19 PM

Ain’t it fun?....mistakes and all.

When making parts, like for a raised panel door, I always make an extra piece, just in case.

Also, I find it helpful to take five minutes to do a full scale drawing of smaller projects on the back of some 1/4” plywood. You can visualize it better and verify your cut list from the drawing.

Even so, I don’t cut All the pieces to length until needed, as mentioned by others.

-- Mark - I prefer the tumult of liberty to the quiet of servitude.

View bondogaposis's profile

bondogaposis

2524 posts in 1003 days


#15 posted 07-14-2013 12:38 PM

When you cut your pieces to length use a stop on the miter gauge. Cut all of the pieces that are the same length with the same set up. That way the only measuring you need to do is to set up the stop. Most of the time absolute accuracy is not needed as long as, say all of the rails are the same length. It pays to cut an extra part also, so that if you mess one up you have a spare. Measure as little as possible.

-- Bondo Gaposis

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