A basic requirement for accurate lathe work is the precise setting and securing of lathe tools to center height and angular position. When a project requires frequent tool changes, the (re)setting of the tools can become a significant fraction of the total time required as well as an annoyance to the machinist. Several styles of quick change tool holders which allow rapid exchange of tools without loss of adjustment/setting are commercially available. The problem is that these are expensive and are really designed for higher speed, power and size lathes.
The basic plans and inspiration for these tool holders came from an ad in the Home Shop Machinist magazine. [see http://www.homeshopmachinist.net/ ] (They also publish the Machinist's Workshop on alternate months -- 6 issues per year for each magazine)
The ad was for the KRF Company of St. Joseph, Michigan.
[see http://www.krfcompany.com/overview.html ] The KRF Company not only sells the finished tool holders but also sells the plans for people that would rather do it themselves. These are well worth the money in the false starts they will prevent.
Manufacture of these holders not only increases our machining capabilities but provides our students with practice in squaring stock in a milling machine, precision layout, use of center finders/wiggelers and edge finders, drilling, tapping, precision boring, and slitting saw operation.
Our first tool holder constructed was for carbide tooling and threading which
requires zero back rake. This was constructed of 1 inch X 2 inch CRS that
was available. This was machined before a set of the KRF plans was
purchased. While it is fully operational, and is frequently used, several aggravating
details such as using machine screws sized so that two sets of hex keys (Allen
wrenches) are required could have been avoided with the KRF plans.
The second type of tool holder was one with 7.5 degrees of built in back
rake. This eliminates the need for considerable grinding and avoids cutting the
tool bit in two with repeated sharpening. This also provides an easy
way to obtain back rake on brazed carbide tools. While not practical or
desirable on the higher power and higher speed commercial lathes, positive back
and side rake is beneficial for the lighter lathes. The major problem our
students have with this holder is remembering to grind additional end clearance
on the tool bits. this holder was machined substantially in accordance with the
KRF prints, and is considerably smaller and more handy than the 30 degree right
threading holder. The screw sizes specified allow the use of only one hex
key set to adjust the holder and bits.
<pictures of back rake holder goes her>
The third type of tool holder produced was a boring bar holder. The particular bar shown is 1/2 inch in diameter and takes 3/16 square tool bits.
Several of our students with home lathes or who are employed in machining operations with limited equipment budgets have chosen to make a series of tool holders, indexing plates and tool posts for their lathes as one or more of their projects.
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last updated by GmcD on 19-Mar-11 19:30
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