# Digital level opinions

### Help Support HomeBuiltAirplanes.com:

#### Pops

##### Well-Known Member
Log Member
In building the Cleanex we used several different levels ... a couple of good bubble levels and a SmartTool Level:

View attachment 47092

It must have worked as the airplane goes straight when I take my hands off of it! :grin:

Dale
N319WF
Same level that I have, one of the better tools that I have bought. I would buy it again.

Dan

#### Dan Thomas

##### Well-Known Member
Any time I buy a level, I go to the store and try a few. Set them up against a vertical shelf leg or something, and see what it says. The leg doesn't even need to be particularly level, either; just see what the level says about the leg. Then rotate it so the other edge of the level is against the leg, and see if it says the same thing. If not, it's no good. Do that on a horizontal surface, too. And rotate it end for end in both checks as well. It can be hard to find one that agrees with itself.

So many of these tools come out of countries where quality isn't much of a priority.

#### Little Scrapper

##### Well-Known Member
HBA Supporter
Log Member
Stabila has a phenomenal reputation, I'm sure I'll be happy. I'll definitely let you know my honest opinion when I get it. I've heard about that "smart level" brand, a lot of builders seem to use that one so I'm sure it's decent.

#### Little Scrapper

##### Well-Known Member
HBA Supporter
Log Member
No, it's not necessary. Yes, a spirit level is perfectly fine.

Do I need it to be within a hundredth of a degree? No.

Attached is my latest caliper, a Brown & Sharpe model 579-1that I purchased on ebay for $38 and includes a case. I'd say it's about 30 years old but absolutely flawlessly taken care of. So for about the same money you can get a far superior tool that will out live you and is a joy to use because a pro tool is smooth as silk. Ya just gotta be willing to buy it used. For old school tools, I agree. I bought a lot of B&S micrometers and similar from e-bay. Cheaper than even the cheap stuff sold now and a pleasure to use. Sure, there's a small risk buying anything used and unseen, but so far, I lucked out. I have used to them to check some cheaper digital tools and try as I might, I can't detect any inherent flaw in their accuracy. No, they just don't feel as nice and silky-smooth to use, but I seem to get acceptable results from them too. #### Dan Thomas ##### Well-Known Member I have two digital calipers. Both were less than$40. The older one is bang on, checked against micrometer gauging slugs. The other ($20) is off by a half thou throughout its range. Either one is plently close enough for aircraft construction. My old vernier caliper was no more accurate than that and cost me a lot of money at the time, and any dial calipers I had would get debris in the rack and derail the pinion gear and make far too much trouble. Sometimes we think that because the machinery is available, we have to use it. Just like medical equipment and drugs that can keep us alive far beyond any sensible limit, and costs everyone an obscene of money trying to stave off the inevitable. Striving for such precision can also lead to extra years in the build process, and many rejected parts that were perfectly acceptable. Weight is far more important than precision to .001" or a tenth of a degree. The aft fuselage and sternpost of my old Auster, a certified factory-built military airplane, was off to the right three inches, and I had never noticed anything in flight. I have seen some pretty extreme errors in modern certified airplanes too, and they still fly OK. That said, get the wing and tail rigging as close as you can. Some homebuilts have crashed on their first flights because the wings were so far off they were uncontrollable. And the washout built into a wing should be really accurate. You might be able to rig out wing-heaviness, but a difference in washout will still make one wing stall sooner. #### Rockiedog2 ##### Well-Known Member Job for a digital level. When building the wings for the SSSC. I set my building table with a transit and a level. Built the first wing and no twist checking with a digital level. After I built the second wing, it had a slight twist in the outer 4 feet . Checked the table and it had the exact same twist. Somehow the table must have got bumped and I didn't know it. I should have checked it before building the second wing. In test flying the airplane, it had a heavy left wing, and with the geodetic type of construction the wing can't be twisted . Just like an all metal or wood skinned wing. I got to thinking about the way Cessna adjusts the rear spar attach bolt in the 150/172's. The wing spar attach bolt is inside a bushing with the bolt hole drilled off center. You can loosen the attach bolt and turn the bushing with a wrench and raise or lower the rear spar about 1/4" up or down and re-tighten the bolt. So I decided to lower the rear spar attach fitting, but how much? My airplane is all wood with a wood rear spar carry thru, with a 4130 steel straps from one side to the other side that bolts to the wood spar carry thru. All I had to do is make a new set of straps and drill the hole for the spar attach bolt down the needed amount. How I found the needed amount. If the twist is in the outer end of the wing, it will have more "arm" and leverage than if it was in the middle or the root end of the wing. Each wing minus the wing tip is 12' long, so I measured the wing with the digital level at the root (0) and at 4'-- 8' and 12' stations. I multiplied the degrees and the stations to get a "foot/Angle". Added all the F/A on each side for a total. Now I need to have the same F/A on each wing and the airplane will not have a heavy wing while flying. So I had to add 2/10 of a degree for each station of the left wing to equal the total F/A of 105 on the right wing. Using the distance between the front and rear spar, I had to lower the rear spar attach bolt .058". Now in test flying in dead smooth air the left wing is very, very slightly heavy. .060 would have been right on. So I put a small trim tab on the aileron with very slight bend and now I have flown it 50 miles in smooth air with out touching the stick. I don't know if anyone else has ever done this the same way, but it works. I know it can be done without a digital level, but it makes it easier. Dan Right on. Like Pops says there are lotsa uses for the digital. Another one he didn't mention that I think is a good example. When setting the dihedral during the construction phase all we gotta do is place the digital to the wing and shim til it says the correct degrees then build the struts to fit that. Forget the length for the struts shown in the plans except for a xcheck. Takes all the math and such out of it. I won't be going back to anything like that. Same deal with the angle of incidence and all sorts of other places...IIRC the Pitts rigging tolerances were 1.5 degree. With a digital no reason we can't more easily get it dead on. I was having trouble getting my RV8 rigged. Found it in no time with the digital..the left wing had .3 degree twist in it.(that wing came here fini by the factory; I got it rigged but it never did feel really hooked up like I expected). I learned there may be some technique involved when shimming/remeasuring with the digital. If we place say a 1/16 shim under the part we're shimming while just barely lifting the level then set it back down it may not register the change accurately at least with my ancient one. So I take it off the part and give it a wag then set it back on it. I got at maybe a dozen levels around here...don't ever stack em on top of one another. It'll drive you crazy. LOL Last edited: #### Pops ##### Well-Known Member Log Member Reminds me. One time at work in the mid 1980's, Quality Control at the company where I worked had a large machined surface block of steel that weighted about 20 ton. One corner of the 1' thick of steel was turned up .060 from setting a long time while not supported correctly. They wanted it level. It was setting on jacks in about a foot square grid. I used a machinist level and checked and marked the part that was turned up. Set a 10 ton die on the level part and then a 5 ton die on the turned up part. Then I loosened the jacks under the 5 ton weight. Told the department head to turn the heat up to 95 degs on the furnace during the night time when the building was closed. Then early in the morning set the temp back to normal. I checked the steel every day, took about 2 weeks fluctuating the temp up and down to get the machined surface level. Dan #### ekimneirbo ##### Banned Ekimneibro, as far as dial calipers I tend to disagree with the$15-$30 cheap caliper. Most are junky and not a long term tool if used frequently. I own probably close to a dozen of them and most are high end machinist grade tools. Fortunately, you can buy near mint condition professional calipers on ebay all day long for under$50.

Attached is my latest caliper, a Brown & Sharpe model 579-1that I purchased on ebay for \$38 and includes a case. I'd say it's about 30 years old but absolutely flawlessly taken care of. So for about the same money you can get a far superior tool that will out live you and is a joy to use because a pro tool is smooth as silk. Ya just gotta be willing to buy it used.
I think we have some things in common when it comes to how we view tools and being accurate. I consider myself to be a toolaholic and not interested in any rehabilitation programs. I agree with you that brands like Brown and Sharp, Mititoyo,etc are better quality. You save by buying used quality and I agree that's a good idea if you take the time. Now here is where you may disagree with me. The quality brands are not really any more accurate than many of the cheepos. Yes you can get some that are poorly made, but for the most part they do a good job. Then when that little piece of grit finally gets into the gear rack....you throw them away cause they are cheap. Accuracy wise they do just as well as the expensive ones. Something to consider here is that while a dial caliper is called a precision tool, it basically isn't. It's kind of an oxymoron. They are usually used for a quick check on something that has a two place decimal tolerance. That's still kind of precision, but to most machinists its a non-challenge and something usually speced for fabrication work. While a dial caliper may read in .001 increments, it isn't used to check parts with a .001 tolerance. That's why I feel that whenever someone uses them in airplane fabrication it is fine with less expensive ones. I do feel as you do about trying to do things to that best of your ability...always.
I remember when the digitalcalipers first became available. Everyone wanted them....it was new technology....it took away the chance of misreading the dial....it was just the newest best and most accurate....or so it seemed. They failed regularly and quickly fell out of favor. Back t!then they were really expensive. Luckily my employer paid for them. Personally I would never have a digital caliper again.
Sometimes the old stuff was marginally accurate....like the mechanical calipers Dan referred to, or the opposite extreme, the super mic . When you start getting into real precision work, environmental issues come into play. Take a piece of aluminum. It will expand more as it warms than the steel that your measuring tool is made from. If you mic the aluminum at 33 degrees and then set both the aluminum and the mic outside in the sun on a hot day, you should see a difference in the reading. Do the same with a caliper and you probably won't notice any difference. So, a caliper is called a precision tool but it really is more for larger tolerances, and that's why I think the cheepos are fine......but if you can find used quality tools cheeply....that's even better.

Question? How did you determine the Johnson level was bad ? How far off was it ?

I never tried it, but I wondered if the best way to check a level might be might be to get a piece of wood that was planed to an even thickness and cut it cross way to make two pieces. Then set them in some water so thy float and set the level on them and see what it reads.:gig:

Last edited:
2