method of mounting tooling on a mill/drill

[darryl]

Just was milling a gearbox and realized I was cranking the head up and then down each time I changed a tool- drill chuck, end mill holder, fly cutter. Each time I had to crank the head up, make the change, then crank it back down. Getting kind of tired of having to do this, I thought why not make a sort of universal holder that would mount to the spindle, which would then take a low profile, universal type of mount. These mounts would carry a variety of tool types (one would take the drill chuck) and would slide in sideways, then be locked in place.

My spindle takes an MT3 shank, and I've made up a couple pieces of tooling that has both that shank and a flange that's machined to be a tight fit onto the end of the spindle. These tools are noticeably more rigid than any of the MT3 shank tool holders alone. For me, the universal holder would be a progression in tool holding, and it would not interfere with the use of any of my existing tooling. I realize I would have to make the holder and the inserts, then machine each insert for the tool I want it to have. This isn't much different than having a special toolpost for the lathe, with all the various tools pre-mounted in individual holders- this would simply be the mill version of the same thing.

I suppose there might be such a thing already, but I don't recall ever seeing it. I think maybe there are things like this made for larger, more expensive mills- some of the automatic tool changers look to be a step in this direction.

You could all say get a bigger and better mill, with a better type of tool holder, but that's not going to happen anytime soon here.

[mattthemuppet]

Why not make a bunch of mt3 spacers of different lengths then plan out the total z required and for each tool. Similar amount of work (I think) and not tied to individual tools. I have a similar issue with center drills and jobber length drills on my drill press.

[dian]

"would slide in sideways": it woud be interesting to see, how you plan to do that. why dont you just crank the table out of the way? or power up your z?

[justanengineer]

Stick a 1/2" collet in the spindle then change the arbors on your tooling to straight shank 1/2". Barring this, build a rapid traverse for the Z axis.

[MrFluffy]

Anything you don't have to crank up and down to change will be prone to falling out if it works loose. I've had the 40 taper on my mill work loose once or twice during heavy cuts, and I have had time to stop the machine on the clutch and sort it out before too much carnage because the taper held it roughly in position. And I have to crank the knee up and down to change tooling just the same. The best I can do is the taper is so fat you don't have to crank as far to release it as you would a morse. Even a clarkeson autolock or weldon shank cutter has to come out downwards for these reasons.
Not sure I want to see the carnage that would have resulted if it could come out without a taper or fixing retaining the shank at least a little when it works loose.

[danlb]

Mills provide a very precise mounting system. One way to accomplish that is to use surfaces that mate which are separated by some distance. To illustrate on a huge scale: An 8 foot long rod with a 1/8 inch taper over it's length will be a close fit to a straight hole and a fraction of a degree from parallel with the bore. A 4 inch rod with a 1/8 inch taper will be several degrees off and will rattle around in the bore.

Scale that down to thousandths of an inch taper and it becomes apparent that more precise tapers are required to make a short tool holder that provides the same axial precision.

Given that.... You need a system that changes the tool in less than the length of the quill travel. You also need tools + tool holder that are all the same length.

If you use an ER40 chuck you can make tool holders that have a 1 inch long 5/8 inch stub that fits in the chuck. The er40 chuck will grip the whole length of the stub. Then all you need is to cut all your drills to the same length and then make tool holders for your end mills that make them the same length.

I think that will work. I just crank things up and down or back and forth a lot.

Dan

[Paul Alciatore]

I also have had thoughts on this in the past. Yes, one of the problems with any tool holding system for a mill is the axial alignment, both in terms of run out and also angular alignment. Either or both of these factors can be off. Another factor, if you want to be able to make identical parts, is you want vertical position (along the direction of the axis) to remain constant also.

Tapers normally use a relatively long length to meet the run out and angular requirements and are a compromise for the vertical positioning requirement because the act of tightening them in place involves vertical movement. When changing tools, maintaining the vertical position within +/- 0.001" is challenging and within tenths is almost impossible.

Just thinking here:

A long length is not the only way to accomplish the axial alignment. You could substitute a wider diameter AND a short, central pin with a high accuracy, tight tolerance, fixed diameter. The pin, which would have to be high tolerance because it is not a taper, would take care of the run out and a mating surface at a larger diameter would control the angle and longitudinal axial position. Here's a concept drawing:



Notice that it substitutes a high accuracy, central hole/pin for the more normal taper. This gives each feature only one alignment task, not multiple ones as in the case of a taper.

[Rosco-P]

Install a rapid lift mechanism for the head and a power drawbar.

[Joe_B]

Install a rapid lift mechanism for the head and a power drawbar.

^^ This

I have tried ER collets and many other things but finally designed a lift and a captive drawbar and just use R8 collets. Never looked back!

[J Tiers]

You will NEVER get a close tolerance straight fit to last.... and it will never be as good as an equally well-done taper fit. It's the same issue as with the mythical parallel section "register" on a spindle....

Just to assemble a straight fit you must have clearance. And the total mis-position will be double the radial clearance. You start out way behind, and can never catch up due to wear.
If you had a tight metal-to-metal fit, you would also need a hammer to assemble and dis-assemble the fit, which will soon be a very poor fit due to galling and wear. An exact zero-clearance fit is nearly impossible to make other than by chance. You will nearly always have either an interference, or some clearance.

By contrast, a taper allows a tight metal-to-metal fit, but still allows trivially easy removal and replacement.

There is just no contest....

The ONLY straight parallel fit that works on a mill is the shrink-fit holder. The fir is between the tool and the holder. There are a few problems with that shrink fit as a way of assembling a holder to a spindle, though....

[loose nut]

It's the same issue as with the mythical parallel section "register" on a spindle....

Is the the one that has the myth about how loose fitting threads on a spindle will align a chuck accurately without some sort of register.

[Arthur.Marks]

The fact is, there are sophisticated systems (example) with low mounting/release depth, quick change capabilities and repeatable tool lengths, but they are much too expensive for use on a mill/drill. Then there is the Tormach TTS system. Remember, the Tormach is already designed for the same MT3/R8 spindle as on a mill/drill. It is also designed around a reasonable price point. Take your pick

I can't say I've come across a system that clamps to to the spindle and/or quill OD -- excepting the external taper on SIP jig borers. I don't believe that particular design would save any cranking up/down of the head. An interior drawbar is still used with a central, threaded shaft on the toolholder.

[boslab]

Are you on about some sort of dovetail thing? Like a coupling with a dovetail or coming up with your own short wide taper?
Mark

[Paul Alciatore]

J, I totally agree with you on the fit and wear factor. My suggestion was for a practical device for use in a small or home shop ("Home Shop Machinist"). The other side is that a taper has little longitudinal repeatability. As it wears it will seat further and further back in the socket. So it will be impossible to get repeatability in that direction.

There are other options, but they would require more depth which would mean that more space would be needed to mount the tooling. And they would be more complicated and expensive to implement. Perhaps someone could design a very short (less than 0.5" long) collet style clamp that would retain good run out while also gripping a short stud. It may even replace the threads or other holding element I showed on my drawing.

Another thought would be a steep taper, perhaps at 20 or 30 degrees. That would split the difference between axial and radial mounting errors. But it also would be a compromise, especially when it is made real short as the OP would want.

Then, perhaps a three point mount could be devised: one point would be completely constrained in three dimensions. The second point would be limited to two, longitudinal and rotation about the center axis, and the third would be limited to longitudinal only . With a drawbar to pull the holder tight into these three points. But, with only three points of contact, it is going to lack rigidity. And there will be problems with the detailed design of each of these points.

No matter what you do, there are going to be compromises. Oh, hardening would help with the design I showed and probably with any other design.

You will NEVER get a close tolerance straight fit to last.... and it will never be as good as an equally well-done taper fit. It's the same issue as with the mythical parallel section "register" on a spindle....

Just to assemble a straight fit you must have clearance. And the total mis-position will be double the radial clearance. You start out way behind, and can never catch up due to wear.
If you had a tight metal-to-metal fit, you would also need a hammer to assemble and dis-assemble the fit, which will soon be a very poor fit due to galling and wear. An exact zero-clearance fit is nearly impossible to make other than by chance. You will nearly always have either an interference, or some clearance.

By contrast, a taper allows a tight metal-to-metal fit, but still allows trivially easy removal and replacement.

There is just no contest....

The ONLY straight parallel fit that works on a mill is the shrink-fit holder. The fir is between the tool and the holder. There are a few problems with that shrink fit as a way of assembling a holder to a spindle, though....

[Paul Alciatore]

Another thought: reverse the spindle and tool holder labels on my sketch so the central pin is on the spindle. Now, make a collet like mechanism that would expand that pin as the tool holder is tightened so it allows centering while still having a few thousandths of clearance while inserting that holder. A heavy spring would be used in the spindle adaptor to allow some over-travel in this expanding action. Use a square thread or a drawbar to tighten and hold the tool holder in place. That may be the best of all worlds.