Alignment for heavy fixtures

[A Disho]

Due to the kind of product I measure , we use very large size fixtures , much between 200 to 400 lb( 1 to 2.5 meters long). we have NO crane to lay the fixtures on the CMM surface plate,we use foreklift to do so, I got the edges of the surface plate damaged, by forekilft and when pushing/dragging the fixture on surface plate,
Know I put some 2.5 x 2.5 wooden blocks undernieth the fixture while I do inspection layout for my parts,the alignment for 95% of my fixtures done on the Tooling Balls( SPHERES).
Do you think there will be much error or difference in this kind of set up and alinment, and what is the best way to handle large size fixtures like what I deal with.


Thank you in advance

[ag162]

Hello,
As long as the fixture base is solid enough as to not bend or warp, everything should be ok. Make sure that there is no movement from uneven blocks. The alignment will compensate any skew in the base. I worked with fixtures that were built on die sets and we used a forklift to put them on our cmm also.

A.Gore

[Jeffrey Lovely]

I used wood blocks one time
one time only
created alignment one day
next morning gage had settled
try holding a net at .05 mm
when the gage sunk .25 !!!!
use steel blocks
I took I beam cut up to 8 pc
and had them machined

[Bill **********]

I work with gages MUCH larger than what you are working with and I don't have a crane either. I load and unload everything myself and I'm VERY careful of the surface plate. I typically tip the forks forward until the gage feet away from the hilo touch the table and then set a piece of oak 4X4 under the two outside feet closest to the hilo. I then easy the gage down onto the 4X4s and back the hilo out until I can use it to lift the gage off of the 4X4s and remove them. Then I set the gage down very carefully. I just had a gage in here that weighed 3500 lbs and I work with larger ones than that. Just be VERY careful while placing and removing them and you won't tear up your granite. As far as setting gages this size on wood, I would NEVER even attempt to measure something this size sitting on wood. Everything goes directly onto the granite AND I clamp it as well. Sometimes I have gages that I can't set directly on the table using the method I described and for those cases, I had the fixture builders build me some 6X6 match ground stand offs that I can use to set the gages on. I would Highly recommend using SOLID stand offs instead of wood.

Bill

[ag162]

3500 lbs?????? Wood is definately not advisable for that. And I thought I had some heavy fixtures. Our situation was easy to work with. I had a stand up forklift and our fixture bases had eye bolts. With straps, you could handle them very easily and never damage the granite.

A.Gore

[kbotta]

A GD&T instructor once told me about a test that NIST had done. It was part of the 'freestate variation' ideaology.
NIST took a 6' steel I Beam measured it in the middle and got 'X' number. Then they took a penny an placed aside the point of measurment and got 'Y' number. Took it off, and got 'X' number again.
All this with a penny.
While this is extreme, imagine a very heavy gage supported by 4x4's. that can not be good.
A rule of thumb is this: Check it as it is to be used.

HTH,
Kev

[george frick]

isn't there a weight limit to load on the cmm's?

[Bill **********]

Al,

I do primarily very large gages. Entire hood assemblies, 4 door removable hard tops, pickup truck dually side panels and things of that nature. This 3500 lb gage isn't even that big for me size wise. Thats probabaly about as heavy as I work with, but it wasn't that large of a gage. It was for an 18 wheeler truck door and the entire base was steel.

Bill

[kbotta]

Bill,
You guy's build that?
Kev

[Bill **********]

Kevin,

Actually that was an engineering change that we did but we build gages that size and larger. My little machine is a 9-15-9 my big boy is 20-33-25.

Bill

[Mr.Natural]

A Disho,
95% of our fixtures are heavier than 1000 lbs. DO NOT use wood under these things, it will settle no matter what you think. I have even see wood blocks disintegrate under the weight of these fixtures. As far as the bases twisting, belive me NO matter how sturdy these things look & no matter how much webbing they have on the bottom side they will twist/warp, level these fixtures & use all of the jack screws & make sure all of the pads are in contact with the table. As far a forklifts loading & un loading them..... BE CAREFUL !!!! I've had em do it & sooner or later they will put some pretty big grooves in the table. You really need a crane to move position them.

[ag162]

Bill,
Side panels and Hood Assy's sound like fun. The largest I have worked with are heat shields aprox 2' x3'. Ironicly the heavier fixtures were for small brackets. The die sets held both left and right hand fixtures. Right now, we build small brackets. Most can fit in one hand. The company I start with next monday is about the same. The drawback is that the programs are always short and fast running.

A.Gore

[Hilton Roberts]

At the last place I worked, we measured 3000 lb cylinder heads for diesel engines and we tried setting the heads on oak blocks. Didn't work. The blocks were pretty solid but they did move and it was detectable. We ended up setting the heads on steel adjustable blocks and that solved the problem. We were fortunate that we had a pendant lift to position the heads so we did not have to use a motorized lift. Still have to be real careful.......

H

[Bill **********]

Al,

Sometimes it takes me a week to write an entire program and during the final it may take the better part of a day to run. They are fun and challenging. We do smaller gages too but it always seems like I'm just getting started and the job is done.

Bill

[kbotta]

Bill,
I was in Indiana and my family made my aunt sing for us (she is like 65 now, used to open for Loretta) any way, after she sang - the guy next door busted out his banjo and went to town. We were all just sitting there quiet and in awe. It was awesome...
Kev