FILENAMES: 7x10holder0.jpg 7x10holder3.jpg DESCRIPTION: These are pictures of a shop made lathe tool holder. Posted by James Waldby . The following description was provided: ================================================================= The first of these two pictures illustrates a tool-holder for using TNMP 321 or 322 carbide inserts with 7x10 mini-lathe. The second picture shows how I modified one side of the tool post so that the tip of the insert is at spindle-centerline height without shims and without the holder being too thin. I haven't broken or chipped any inserts in my experience with this holder so far, vs. chipping quite a few inserts when using a 1/4" indexable set. TNMP 321 and 322 inserts are inexpensive and easy to find on eBay and from carbide cutter suppliers. See http://www.icscuttingtools.com/catalog/page_307.pdf and http://www.carbidedepot.com/formulas-insert-d.htm for insert data. Briefly, a "TNMP xyz" insert is a triangle large enough that a circle of diameter x/8" can be inscribed on it; it is y/16" thick; and it has corner radii of z/64". Also see http://www.metalwebnews.com/howto/toolholder/toolholder.html for Ted Edwards' presentation on tool holders for TNMP inserts. The principles of my tool holder are the same as shown in Edwards' drawing http://www.metalwebnews.com/howto/toolholder/drawing.html except I used 5/8" bar rather than 1/2" and also modified my tool post. The holder illustrated in 7x10holder0.jpg was made from 5/8"-square bar by sawing away a slab of metal at the top front at an angle of 5 degrees, with two cuts, then sawing off the lower front corners with two more cuts, then drilling a hole and threading it #6-32 for the insert attachment screw. Of course if you have a mill you can mill instead of saw. I used a DTI when setting up the saw cuts on my $200 HF bandsaw and got close to what I wanted. Tip thickness measures ..268" on caliper. This holder is a little shorter overall than it should be, and this one requires a 5-degree angled block above the insert because the threaded hole for the #6-32 bolt is straight up and down. The angled block was scrap from the first cut. When long chips are coming off they sometimes catch on the block, so I think of this as a prototype rather than a finished version. In a later version I plan to (1) drill the hole at 5 degrees; (2) use a shorter cap screw; (3) possibly put left- and right-oriented inserts at opposite ends of one holder; (4) make it at least 1/2" longer; (5) mill .07" - .09" off the seat of the tail of the holder, allowing its head to be that much thicker or to fit in an unmodified seat. The thickness of the front tip of the new holder is the sum of four numbers: a) centerline height; b) tool post seat height change; c) point projection correction; d) minus insert thickness. On my lathe this is .3125 + .070 + .011 - .125, or .2685", as follows: a) On my 7x10, the centerline is about 5/16", or .3125", above the original tool post seat level. b) As shown in 7x10holder3.jpg, I milled away 0.070" of surface on one of the four seats of the tool post. I did this milling with an endmill in a three-jaw chuck on the lathe, in several passes, raising the tool post and the seat being milled about .008" each pass. I supported the tool post as evenly as I could with several stacks of washers. On each pass I took out one .022-thick layer and added in one .030-thick layer. I meant to mill off only 1/16" but instead ended up changing the seat height by .070". c) The point of the insert projects 1/8" beyond the tip of the holder, so requires a height correction of sin(5 degrees)*1/8", or .011". That is, the bottom of the tip of the insert is .011" lower than the tip of the holder. --end of text--