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Aftermarket dual contact?

mhajicek

mhajicek

Diamond
Joined
May 11, 2017
Location
Maple Grove, MN, USA
What's the feasibility (and what are the complications) of converting a standard steep taper spindle to dual contact? I seem to recall hearing that this can be done for a 40, and it follows people would want to for a 30. I'm hypothesizing about doing it to an ISO-20. I'd have to get custom holders too, or modify them. Is it just a matter of putting shims on top of the collar, precision ground to match the gap to the spindle nose?

Thanks
 
I think we've had threads where ad hoc mods have been made to get this feature, can't point to anything ATM. In theory it can be done, but you want something dead-reliable, a failure of a shim/spacer could destroy a spindle or worse.

If I wasn't going hog-wild with the mod and commissioning someone like Mari-tool to make some custom "hi-flange" holders that I could grind myself to match the existing spindle, I'd want a spacer that was so well integrated into the spindle face that it could not come off. Some spindles use a ring of balance holes at the nose (tapped for weight set screws), I'd mate to them but it would require a rebalance.

Let us know what you find out...
 
barbter said:
But as yours is a HS spindle and thus not much torque, would you actually benefit?
Click to expand...

Advantage is preventing "suck in" from high spindle speed opening up the taper.

Disadvantage (setting aside fussing the face mate to the right value) is spindle will still expand, too much and there's radial clearance between holder and spindle.
 
On the 50K RPM CM-1 I've found that dynamic roughing 17-4 H900 with a 3/8" puts spindle load at around 100%, and works ok for several minutes at a time. This is pushing the rigidity limits for the spindle. I'm hoping to improve the rigidity of the spindle/holder connection to improve tool life and finishing, and to allow slightly longer stickouts. As I understand it, a dual contact 40 is almost as rigid as a 50, and a dual contact 30 is almost as rigid as a 40, so it would stand to reason that a dual contact 20 should be almost as rigid as a 30.

I haven't noticed any "suck-in" issues running at 50K yet.
 
Thought for kluging it, since I would only need it for one holder. I could take an ER-20 holder (they don't make anything other than ER holders in ISO-20), drill and tap the flange for 8 set screws, put it in the spindle, and snug some flat point set screws against the spindle to some appropriate torque, with Loctite on the threads. After it sets, it should repeat. Won't be as rigid as a proper conversion, but should be better than stock, and I shouldn't have to worry about balance at the RPMs for that 3/8".
 
If it's just one tool, you could grind the taper down until the flange contacts. Might want to touch the flange to make sure it's square (then grind the taper some more :) maybe hit the flange first) ... something like a Brown & Sharpe 13 would be ideal but lacking that there's the ol' tool post grinder approach. Retention stud might need a tiny bit of modifying too or just shorten up the skinny end of the taper.

If it works, make more. If not, just another experiment that didn't pan out.
 
mhajicek said:
As I understand it, a dual contact 40 is almost as rigid as a 50, and a dual contact 30 is almost as rigid as a 40, so it would stand to reason that a dual contact 20 should be almost as rigid as a 30.

I haven't noticed any "suck-in" issues running at 50K yet.
Click to expand...

I think you have the connection and then you also have the bearings and the rest of the machine.

IMO 30 and 40 taper are not that far apart. 50 taper is huge in comparison. And 50 can do wicked neat stuff, albeit at a lower RPM. All I'm saying is each connection has a purpose and dual contact doesn't transform a machine into something else.
 
You also really need more drawbar force for dual contact, well to get more of the achievable gains you do. I wonder what the tolerances would be on your 20 taper for the face contact? I REALLY think this is beyond reason for what you want. To do it halfway right I would bet that the work and cost involved is way beyond the gains.
 
mhajicek said:
As I understand it, a dual contact 40 is almost as rigid as a 50
Click to expand...

It's a common misconception. The benefit is actually much more subtle than that.

Under the right conditions, you may see a 20% improvement. In others, no improvement at all. It depends on where the limiters are in a given application. The main limiter might be the spindle bearings, in which case changing the toolholder interface will have no net effect.

Not all spindles are created equal, and I've used some pretty crappy CAT50 spindles over the years, some of which were weaker and less rigid than our DMG Mori CAT40 HMC spindles. But then I've also used some really good ones, and there's really no comparison. Good CAT50 vs good CAT40 is like comparing CAT40 to R8.
 
Orange Vise said:
Not all spindles are created equal, and I've used some pretty crappy CAT50 spindles over the years, some of which were weaker and less rigid than our DMG Mori CAT40 HMC spindles. But then I've also used some really good ones, and there's really no comparison. Good CAT50 vs good CAT40 is like comparing CAT40 to R8.
Click to expand...

Much like the video demonstrations I see of better (bigger) 40 taper spindles when compared to a Haas cartridge. Some seem to have damn near twice the outer diameter of a Haas, and dang if they don't sound quieter and more stable when taking heavy cuts.

I wonder why that is?...
 
Just as an opinion from the sidelines I think dual contact in a Cat is way overrated and never proven real world.
It is a very great marketing tool and sure seems like a good idea.
As Alice was told..Pay no attention to the man behind the curtain.
I expect many fans to think me wrong so I know saying this is asking for arrows in the back.
Bob
 
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