Every first article at Kalder is measured twice. The first pass happens on the machine, with a touch probe, while the part is still clamped and still warm from the cut. The second pass happens forty minutes later in the metrology room, on a CMM, at 20 \u00b0C.<\/p>\n
People ask why we bother. The probe on the machine is good. The operator knows the part. If the numbers are in, why walk it across the plant?<\/p>\n
A 400 mm steel housing that has just been machined is somewhere between 24 and 28 \u00b0C. Steel grows about 12 \u00b5m per metre per degree. On a 400 mm bore that is roughly 5 \u00b5m of growth per degree of temperature the metrology room never sees. The probe is honest about what it measured; it just measured a warm part.<\/p>\n
The difference is usually 6 \u00b5m. On an H7 bore that is a third of the tolerance band, spent before the customer opens the box.<\/p><\/blockquote>\n
Most of the time the cold measurement confirms the warm one, and the part is fine. Occasionally the cold measurement says the bore has closed up to the low limit. That is the batch we would have shipped out of tolerance on the strength of a single reading.<\/p>\n
What the second reading changes<\/h3>\n
The cold reading is what goes on the dimensional report. The warm reading is what the operator uses to correct the offset for the next part. The two numbers together tell us how much this particular geometry drifts, and that offset is stored with the programme so the repeat order starts where the last batch finished.<\/p>\n
It costs us forty minutes per first article. It has saved us from re-making three batches this year. We will keep measuring twice.<\/p>\n","protected":false},"excerpt":{"rendered":"
Once on the machine, once in the cold room. The difference is usually 6 \u00b5m \u2014 and sometimes it is the difference between a batch and scrap.<\/p>\n","protected":false},"author":3,"featured_media":32,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[3,4,5],"class_list":["post-41","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-metrology","tag-cmm","tag-first-article","tag-tolerance"],"_links":{"self":[{"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/posts\/41","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/comments?post=41"}],"version-history":[{"count":0,"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/posts\/41\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/media\/32"}],"wp:attachment":[{"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/media?parent=41"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/categories?post=41"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/preview.industrial.anpsthemes.com\/demo13\/wp-json\/wp\/v2\/tags?post=41"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}