These pages describe the construction in my home machine shop of a series of engineering projects, primarily in metal, including the Hodgson 9-cylinder radial engine, the Wren Turboprop, a CNC bench mill, and other engine, shop, and electronics projects.
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|22 Aug 2005: The big order from The Little
Machine Shop has arrived! On August
15th, just last week, I had posted some musings (see the Old News page) on yet
another spindle configuration, this time a
performance-tweaked R8 mini-mill spindle. With all of my
other spindle experiments, the lack of fixed Z tooling
has been a real headache. Along comes Tormach R8
tooling to the rescue! I first learned of the Tormach
system from the CNC Zone,
and the description and photos were encouraging.
Normally, R8-tapered spindle tooling will have a variable
rather than a fixed Z offset. Even a solid end mill
holder will not always have a consistent Z offset due to
variations in drawbar tension. But the Tormach system
takes a different approach. While not technically QC
(Quick Change), the Tormach tools have a repeatable,
fixed Z-axis offset. With a set of Tormach adapters and
cutters prepared and measured ahead of time, the Z-axis
offsets can be entered into Flashcut's tooling table, and
as the G-code is executed, no resets to program Z = 0
need be done. Hurray!
Here's how Tormach does it. First, a special and very precise ground R8 collet is inserted into the spindle. Unlike a normal R8 collet with a rounded nose, the Tormach collet is slightly shorter and has a flat face. Each adaptor has a 1.500" diameter hollow-ground collar. As the drawbar is tightened, the collet retracts and aggressively pulls the tool's collar against the spindle, rather than the nose of the collet. Since the spindle nose is by definition fixed, the now-secured tooling also assumes this happy, fixed-Z state. When secured, the only portion of the Tormach collet in contact with the tooling is the shank, not the face.
When I begin to collect a set of pretty much anything shop-related, I usualy underestimate my needs. Rather than repeat that again, I splurged a bit and bought the Tormach CNC starter set as well as some additional tooling, mostly further examples of the ER20 collet holder. The box on the left contained the starter set. Shipments like this are always a lot of fun to dig through, clean up, and sort out.
The starter set is a good deal compared to the individual components. Importantly, it also comes with a special ground fixture and a height guage to measure and set the Z-offset of the tool. It even comes with a little granite surface plate! Since I already have a larger granite plate, the little guy will see use with other measuring tasks in the shop.
The picture to the right shows one of the ER20 collet holders, a 1/4" ER20 collet, carbide end mill, and the adaptor nut, detached and to the left of the holder itself. For those not familiar with the ER collets, these are excellent and accurate systems which have a relatively large collapse range, meaning one need not hesitate to chuck a shank which is a bit undersized from the nominal collet ID. This is helpful especially with twist and spotting drills of an odd shank size when you need a shorter and more accurate setup than what you could obtain with a drill chuck.
Shanked tools come in two basic varieties... those with flats to accept a set screw, often called weldon shanked, and plain round, such as a twist drill or a carbide end mill. If weldon shanked, it is usually best to use a set-screw adapter, although if there is adequate shank surface area, a collet is fine. Purely round shanked cutters are best used with a collet like this one. Do not mount a cutter without a weldon shank into a set-screw adapter, or you may enjoy the memorable excitement of having the cutter slip, get drawn out of the adapter, and dig into the work. This results in disaster; broken tools, a wrecked job, and potentially dangerous shards zinging around your shop. It is acceptable to use a set-screw adapter with a plain-shanked tool that experiences very low loads, such as an edge finder, but use care that the set screw does not wreck the shank, making subsequent removal and/or reinstallation of the tool very difficult if not impossible.
I am very pleased so far with the quality of the set. I have not done any tests, and have just started measuring general runout and accuracy, but it looks good so far! If you have priced other spindle tooling such as the Royal R8 QC tooling, or the Kwik-switch setup, you'll already have realized what a bargain the Tormach system really is.
Soon, I hope to begin a new project page on the rebuilding and integration of the mini-mill R8 spindle, belt drive adapter, and the Tormach tooling, with my 5B CNC mill. Hopefully, between the KaVo ultra-fast HF spindle, and the more powerful R8/Tormach setup, I will have all my bases covered! (That's a baseball expression for my Eastern hemisphere friends; it means works good... lasts a long time!)
Take care everyone!