Just because I'm a bit bored this morning while sitting at my desk reviewing documents, I thought I'd review, for my own edification, the user needs and requirements that pertain to the use of a tool post.
For production or repeat work, or in the days before carbide insert tooling, or when the lathe owner only machines one kind of material, the user needs and requirements will be different. These needs and requirements are for me--a hobbyist with limited time who doesn't want to chase faults or spend time making adjustments to tooling, but who can never predict what sort of operations or materials might be the target of the day.
User Needs:
1. The operator will use different tooling for turning to the left, turning to the right, facing, boring, outside threading, inside threading, grooving, machining special shapes, chamfering, and cutting off.
2. The operator will use different tooling for rough and finish cutting while turning, facing, and boring.
3. The operator will use different tooling for boring large openings versus boring small openings.
4. The operator will use different tooling for machining different materials, such as high-speed steel for softer materials and carbide for harder materials.
5. The operator will adjust the height of each tool for optimum cutting, which may or may not be at the exact center of the workpiece.
6. The operator needs to change tooling quickly and efficiently to a previously defined position.
7. The operator needs to change the angle of the tool position for different machining operations. The operator needs to set the tool angle precisely, and then return it to a previously used angle precisely without having to indicate it in.
8. The operator needs to machine workpieces within the capacity of the lathe without chatter caused by loss of tool support or stiffness.
9. The operator must be able to procure the tool post and holders affordably. (Of course, the definition of "affordable" varies based on context and intentions.)
10. The operator needs to add tooling in the future as special needs emerge.
Based on these user needs, I see the following requirements:
R1. The tool post shall accommodate 15 different tooling arrangements. I picked 15 to accommodate all the needed operations mentioned above plus a few variations.
R1a. Each tooling arrangement shall be separately adjustable for tool height.
R1a1. Each tooling arrangement height shall be retained between uses once adjusted.
R1b. Each tooling arrangement shall accommodate high speed steel bits ranging in size to the capacity of the lathe.
R1b. Each tooling arrangement shall accommodate indexable carbide bit holders ranging in size to the capacity of the lathe.
R1c. Tooling arrangements used for boring shall accommodate boring bars ranging from 1/2" to 1".
R1c1. Tooling arrangements for boring bars shall allow tool stick-out to be adjusted in ten seconds.
R2. The tool post shall allow the operator to switch between tooling arrangements in five seconds.
R3. The tool post shall allow the operator to change the angle of the tool position in five seconds.
R31. The angle of the tool position shall be fixed to defined angles such that the tool position is retained or restored to a previously adjusted position within 0.0005". (or whatever.)
R4. The tool post shall hold the tool as rigidly as the cross slide and compound of the lathe.
R5. The tool post shall not exceed $____.
R6. The tool holders shall not exceed $____.
R7. The tool post and holders shall remain available in the market for a period of X years.
Now, reviewing the options, it seems to me that:
a. A traditional lantern toolpost doesn't fulfill very many of these requirements. It is limited to HSS bits and very long setup times. But if it comes on a used lathe already, it's cheap.
The lantern post doesn't do boring bars at all--hence the solid blocks of steel I received used to clamp boring bars in place of the lantern post on my lathe.
b. A four-way toolpost doesn't fulfill Requirement 1, unless one is willing to change "15" to "4" (I'm not). And if one exceeds the need for four tools, it doesn't fulfill the requirements for efficient changes or height setting, and it doesn't work well for larger boring bars.
c. An Aloris-style toolpost doesn't fulfill Requirement 3.1. Every time I change the tool angle, I can't restore it back to the previous angle precisely without indicating it in. This constrains the order of operations. Also, for some, the Aloris-style holder may not fulfill the affordability requirements. But it fulfills the requirements for fast changes, at least 15 tool arrangements, boring bars, etc. The main advantage is in the sustainability department. Being the dominant design means it is well supported in the market, and holders themselves are very much cheaper than the post.
d. The Multifix design may not fulfill R5, R6, or R7, depending on the budget and intentions of the operator, and it comes even less close to doing so than other options, particularly if one actually buys 15 holders. And I wonder about long-term sustainability in the market--knockoffs are still being made but they are not nearly as available as Aloris-style holders. I only found a couple of places to routinely buy them, none of which were as easy as ebay or Amazon (or MSC, etc.). Also, the holders are more intricately designed and made than an Aloris-style holder, and so those will be much more expensive (about 2.5 times as much at usual street prices). But it fulfills all the other requirements.
e. One-off designs may fulfill all functional requirements beautifully, but they won't fulfill the sustainability and affordability requirements for most folks.
As with most technology, the more requirements it fulfills, the more it costs. But as I worked this out, I realized that going cheaper than the Aloris-style holder I bought would have left a lot of requirements unfulfilled that are important to my needs, particularly the ratio of time making chips to the time setting up tools. Example: I machined a special shoulder bolt that I bought from McMaster, so that it would replace the broken hollow bolt that retains the nut for the cross-slide screw on my South Bend lathe. I drilled a hole through the middle of the bolt, chamfered the hole on both ends, tapped it for 1/4-20 threads, and then turned down the head so that it would fit flush on the top of the slide to allow free rotation of the compound. That simple project required turning, facing, and chamfering using the tool post. To turn the tool for chamfering, I either had to loosen the lantern post, which would require readjusting the height, or rotate the compound, which requires digging out the allen key for the two lock screws. But I was able to use only one HSS bit for all the operations. Using a four-way would have required separate tools for turning and chamfering at least. I'm eager to get my Aloris-style post mounted, to say the least.
Rick "much ado about nothing" Denney
