I'm making a ring adapter so that I can run Cat40 tooling in my FP1. Most of the information on the Cat40 taper dimensions is readily available. The only spec I have for the drive key width, however, is from Machinery's Handbook for ANSI B5.18-1972. It lists the width of the driving slot in the toolholder as .635-.645 , a whopping 10 thousandths of tolerance. If I'm reading it correctly, the drive key in the spindle nose is specified as .6252 -.6255. Hard to figure out why the spec on the key is so tight when the slot is so wide. Even if the slot is on the tight side of the spec there is going to be almost .010 of lash.
I don't have a spec for the sk40 toolholder but I do have a drive ring for my FP1. There is about .003 difference between the key and the slot. Certainly seems like tighter fit is better if the goal is to prevent spindle damage in case the taper lets go. Is there a reason the Cat40 fit is loose? I'm tempted to make the keys something like .632 so that if the toolholder slot is at the minimum width the fit would be similar to the SK40.
All this might beg the question of whether a drive ring is necessary. I currently run 40 taper collets with no drive ring and this is as designed. One of the reasons for the Cat40 adapter is to run ER collets and a facemill so I'm thinking that with greater loads a drive ring is good insurance. One other question, any reason to harden the ring? I have access to a heat treat oven and surface grinder but the ring is going to be pretty thin ( < .14 ). It would definitely be easier to mill it to size than deal with distortion from heating and grinding.
Has anyone done this? Any advice?
Thanks
Teryk
I don't have a spec for the sk40 toolholder but I do have a drive ring for my FP1. There is about .003 difference between the key and the slot. Certainly seems like tighter fit is better if the goal is to prevent spindle damage in case the taper lets go. Is there a reason the Cat40 fit is loose? I'm tempted to make the keys something like .632 so that if the toolholder slot is at the minimum width the fit would be similar to the SK40.
All this might beg the question of whether a drive ring is necessary. I currently run 40 taper collets with no drive ring and this is as designed. One of the reasons for the Cat40 adapter is to run ER collets and a facemill so I'm thinking that with greater loads a drive ring is good insurance. One other question, any reason to harden the ring? I have access to a heat treat oven and surface grinder but the ring is going to be pretty thin ( < .14 ). It would definitely be easier to mill it to size than deal with distortion from heating and grinding.
Has anyone done this? Any advice?
Thanks
Teryk
