Recently I purchased a CZ-21. It is just over one week old now. I took it out for a first hunt this weekend and when I cleaned it I noted what appeared to be cracks in the housing coming from the coil and headphone speaker connections and extending an inch or so down the housing.
I contacted my great Dealer, Ron at Windycitydetectors, and I emailed Fisher and asked about the "cracks". After several emails with photos I was told that they are 100% not a problem, they were simply a molding seam. I felt a little better however still had concern since it was so new maybe I should ask for an new CZ.
I called Felix at Fisher today and sent emails of the pictures. He also said this is common in all of the latest batch of CZ housings. It is part of the molding process. That is was not a crack. If it were the pressure testing would have failed. He offered to have me send in the detector but said was a normal finding.
I decided to look at the CZ forum because I remembered EZriders question on cracks. There was a reply from Dave J. He gave a name to what my detector had, "Knit lines" and "they are normal, nothing to worry about".
A quick search of Knit lines and I now understand how they are formed, and thought I would pass this along for all the other folks who will eventually see these lines.
Knit Lines.
Start with a simple fact: resin cools as it is injected into a mold. This is why the leading edge of the resin flow within a mold is always the coolest area of the resin, and, therefore, the closest to solidifying. In a well-designed mold, this is generally not a problem. The exception may occur when the resin flow is divided by an obstacle and then meets again on the other side of the obstruction, for example, the core that creates a rectangular hole in a cover plate. When this happens, you have two surfaces meeting downstream from the obstruction. Ideally, they will meld together to form a solid joint, but if they have cooled too much to meld completely, the result is a knit line.
What has happened to the CZ-21 housing according to this explanation is, as the resin flow went around the gates or blocks that form the hole for the cable connections it cooled enough that when the flow met it did not completely meld together.
This being said you need to focus on the wording in a well-designed mold, this is generally not a problem. "The exception may occur" and in the case of our housing with knit lines it did not completely meld. It sounds as if this can be a normal, but not desirable result. After reading the article it sounds as though deep knit lines can affect the product and result in failure. These knit lines are extremely small so the lack of melding should be superficial. Also Fisher pressure tests every housing and they passed. I have no idea how much pressure they apply and suspect it is tested well beyond the pressure applied at 250 feet under water.
My conclusion is that just as Rick, Felix and now Dave J. have confirmed these knit lines are of no concern. The unit is as good as ones without the lines. They all passed testing and should function perfectly. I was also reminded there is a two year warranty if there is a problem. I will also say Fisher and WindycityDetectors offered to have me send the unit in for their evaluation. I have chosen to not send it in. I agree after my research it should not be an issue.
I hope this answers questions regarding Cracks or Knit lines on the CZ-21 housing.
I contacted my great Dealer, Ron at Windycitydetectors, and I emailed Fisher and asked about the "cracks". After several emails with photos I was told that they are 100% not a problem, they were simply a molding seam. I felt a little better however still had concern since it was so new maybe I should ask for an new CZ.
I called Felix at Fisher today and sent emails of the pictures. He also said this is common in all of the latest batch of CZ housings. It is part of the molding process. That is was not a crack. If it were the pressure testing would have failed. He offered to have me send in the detector but said was a normal finding.
I decided to look at the CZ forum because I remembered EZriders question on cracks. There was a reply from Dave J. He gave a name to what my detector had, "Knit lines" and "they are normal, nothing to worry about".
A quick search of Knit lines and I now understand how they are formed, and thought I would pass this along for all the other folks who will eventually see these lines.
Knit Lines.
Start with a simple fact: resin cools as it is injected into a mold. This is why the leading edge of the resin flow within a mold is always the coolest area of the resin, and, therefore, the closest to solidifying. In a well-designed mold, this is generally not a problem. The exception may occur when the resin flow is divided by an obstacle and then meets again on the other side of the obstruction, for example, the core that creates a rectangular hole in a cover plate. When this happens, you have two surfaces meeting downstream from the obstruction. Ideally, they will meld together to form a solid joint, but if they have cooled too much to meld completely, the result is a knit line.
What has happened to the CZ-21 housing according to this explanation is, as the resin flow went around the gates or blocks that form the hole for the cable connections it cooled enough that when the flow met it did not completely meld together.
This being said you need to focus on the wording in a well-designed mold, this is generally not a problem. "The exception may occur" and in the case of our housing with knit lines it did not completely meld. It sounds as if this can be a normal, but not desirable result. After reading the article it sounds as though deep knit lines can affect the product and result in failure. These knit lines are extremely small so the lack of melding should be superficial. Also Fisher pressure tests every housing and they passed. I have no idea how much pressure they apply and suspect it is tested well beyond the pressure applied at 250 feet under water.
My conclusion is that just as Rick, Felix and now Dave J. have confirmed these knit lines are of no concern. The unit is as good as ones without the lines. They all passed testing and should function perfectly. I was also reminded there is a two year warranty if there is a problem. I will also say Fisher and WindycityDetectors offered to have me send the unit in for their evaluation. I have chosen to not send it in. I agree after my research it should not be an issue.
I hope this answers questions regarding Cracks or Knit lines on the CZ-21 housing.