I am having trouble performing the length check out on my Romer. I have not checked length using the bar in over a year. I recently replaced my 6mm ruby ball (they don't bounce well) and calibrated it with help from this forum. Since I had the bar out already, I installed the 15mm probe and started checking length. The conical seat distance (711.168+/-.040) came in for most of the points but never for all 5 checks. I have tried multiple times with no success. My setup consists of the bar sitting on my granite table, being held down with clay(I was told was sufficient). The arm is situated in the middle of the bar and I attempted many different articulations and also keeping the same position. I just can't seem to obtain an accurate read. The bar hasn't been called since 07' but has only been used one other time and has been sitting on a shelf for the last year. Here are some of the results:
I was having the same kinda problem. But my problem was that we were getting in spec and out of spec with myself and another operator. What I determined was the other operator has a "heavy hand" he would push down while taking the hits. I however would just let the weight of the arm seat the ball in the seat. My length always fell within tolerance. So try to use the weight of the arm and not push down.
I re-calibrated the ball using a sphere that is on our Cordax. With the 15mm tip, Standard Deviation is (.004) and Max Error is (.008). The first length check looked promising but then they took a turn for the worse. The sphere is a (.75005") 19.05127mm.
1st Attempt I articulated the arm at different angles.
2nd, the arm was straight down but at a slight angle for all hits.
3rd, the arm was down in front of the machine, arm 90 to the right, then the left.
4th, the arm was angled outward so that the elbow was pointed out away from the Romer.
5th, I articulated the arm in multiple ways.
I did not push the tip into the cup, just gently placed it and still I cannot get consistant readings.
You should contact ROMER Tech Support. Holding the bar down with clay is not advisable as clay can certainly allow movement of several microns causing you to chase your tail.
Clay is sufficient for a DCC CMM.
However, on a manual CMM, you can't trust clay to hold properly. There should be two holes in the bar for bolts to clamp it down. I try to clamp down the bar with a c-clamp in these areas, and I place a washer under each clamp to hold the bar up off the table. This way if your table is not flat, your not warping the bar to the shape of the table. If you're able to use bolts, that would be good to (still use the washers).
You don't have to overdo the clamp pressure. I usually just grab the bar and give it a firm shake. If it doesn't move, you're good to go.
Our Honda QE Rep brought a hot glue gun with his Faro Arm. He even hot glues his tripod to the ground. I thought it was great! I keep meaning to put in a request for one. Money's so tight right now, I'm afraid it might even get rejected.
