R8 or morse taper 3?

[JasonBModerator @jasonb]

The small Boxford VM 30 has INT30 size tooling, Wabeco can be ordered with it and if you know the right people I think the odd Sieg has been supplied with it.

[SillyOldDufferModerator @sillyoldduffer]

Posted by old mart on 12/06/2020 16:02:30:

Size and stiffness wise, R8 is equivalent to MT4, not 3. …

Not according to my calculations (which are always dodgy!)

Comparing the surface area of the R8, MT3 and MT2 tapers with a CAD package:

MT3 is 6105 sq mm

MT2 is 3304 sq mm

R8 is 2287 sq mm

R8 is bottom of the class! Being short and stubby might make it less likely to bend, but flex probably depends more on the heft of the parent mill's spindle rather than what's plugged into it. R8 could be considerably stiffer in a beefy Bridgeport than a lighter Chinese machine. Especially as it's been suggested some MT machines have been bored out to take R8 without beefing up the spindle.

Always possible I've missed something but looking at the specs the advantage of R8 over MT is quick release and compatibility with other non-MT machines. If speedy tool changing matters, or you own a Bridgeport or similar, go for it, otherwise…

I felt it would be advantageous for my mill and lathe to share the same taper. Good theory, not so hot in practice. It comes in handy occasionally.

Dave

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[JasonBModerator @jasonb]

Posted by SillyOldDuffer on 12/06/2020 17:48:20:

R8 is bottom of the class!

Always possible I've missed something but looking at the specs the advantage of R8 over MT is quick release and compatibility with other non-MT machines. If speedy tool changing matters, or you own a Bridgeport or similar, go for it, otherwise…

Think you may be bottom of the class dave

Always simpler when you have the items infront of you. Pic below shows MT3 end to end with R8 collets and a MT4 sleeve above. gauge dia of the sleeve is less than the end of the R8

And to rub salt into the wounds look how much more metal there is where the R8 taper joins the arbor body compared to MT3

Edited By JasonB on 12/06/2020 18:36:29

[Martin ConnellyParticipant @martinconnelly55370]

Dave, you have completely missed the top register on the R8 collet. The stiffness is nothing to do with the taper but is based on the diameter of the tooling where it is unsupported. The length of the R8 collet with its upper register is comparable to M3 so that will not be an issue in stiffness.

R8 diameter where it exits the spindle about 30mm.

MT3 diameter where it exits the spindle about 24mm.

MT4 diameter where it exits the spindle about 30mm.

Martin C

[Jeremy Smith 2Participant @jeremysmith2]

Also, i noriced some of these chucks have flat ends on the end of the taper – what are those designed for?

Are all morse tapers tapped with a hole one one end to allow for the drawbar? I saw some photos online, but the description failed tp mention whether they were tapped.

[Dave HalfordParticipant @davehalford22513]

flat ends are for drills

[Martin ConnellyParticipant @martinconnelly55370]

There are basically three types of end on morse tapers, flat not drilled and tapped, flat drilled and tapped and tanged (the flat bit sticking up from the taper). The plain flat ended ones are found on things like centres that go in lathe tailstocks where they are ejected by the tailstock leadscrew end. The drilled and tapped ones are for use with drawbars, the drawbar is there to stop the tool dropping out due to cyclic side loading as found in milling. The tanged taper is usually found on drills and reamers where a slot in the spindle allows use of a tapered drift/wedge to drive them out of the socket. The tang is not there to drive the tool, it is purely for ejection purposes. These do not need a drawbar due to the loading being straight up through the spindle axis.

You can buy screw in tangs for when you need to use a threaded tool without a drawbar but with a wedge to drive it out after use. A suitable screw will not work as it is too wide for the slot.

Martin C

[Edward Preston 1Participant @edwardpreston1]

Interesting post, thanks guys, understand a bit more now. When I last used a Mill in school, Clarkson chucks were the fashion, have they been replaced by the ER series now then?

[Martin ConnellyParticipant @martinconnelly55370]

Clarkson and similar such as Vertex posi lock require cutters with a threaded end which adds to the cost. As a result ER which can cope with either plain or threaded cutters and gives acceptable tool holding is a cheaper option for people working with a limited budget. ER also use up less of the available headroom on a small machine. ER does not win out because it is technically better but because it offers value for money and more working space. The ability to hold workpieces in an ER collet is often a reason to buy them as well.

Martin C

[SillyOldDufferModerator @sillyoldduffer]

Posted by JasonB on 12/06/2020 18:30:18:

Posted by SillyOldDuffer on 12/06/2020 17:48:20:

R8 is bottom of the class!

Always possible I've missed something but looking at the specs the advantage of R8 over MT is quick release and compatibility with other non-MT machines. If speedy tool changing matters, or you own a Bridgeport or similar, go for it, otherwise…

Think you may be bottom of the class dave

Always simpler when you have the items infront of you. …

Who me, get it wrong? Never happened before!!!

Maybe this is my Waterloo and I shall be off to Saint Helena to think about my crimes! But first, I shall sacrifice the Imperial Guard.

My case against R8 was based on looking at a drawing, not the real thing. The surface area of the R8 taper is small compared with MT3 (and MT2) as shown in pink:

But what's that highlighted in GREEN? If it's a key-way, I'm in the poo again! Of course it's a key-way…

Very educational this forum!

Dave

[John HaineParticipant @johnhaine32865]

Yes it's a key way, but the pegs that engage have been known to break off, and some people remove them. If the cutter jams on a powerful machine it can mangle the peg. Someone posting here reckons that R8 drives perfectly fine without the peg. You can tighten the R8 drawbar a lot without fear of jamming, to a level that the MT would get jammed.

[Michael GilliganParticipant @michaelgilligan61133]

Hopefully within the bounds of ‘fair-use quotation’

… but I will happily remove it if the Moderators consider it to be in breach:

.

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MichaelG.

[JasonBModerator @jasonb]

That's OK with me

Dave I think you should really be looking at cross sectional area not surface area as that is where things will start to flex as anything held on a thin shank will vibrate more than on a thick shank.

[Mike PooleParticipant @mikepoole82104]

The peg in the R8 socket is to stop the collet spinning while the drawbar is tightened. If the taper can spin then the cutter could also spin. The R8 system does not seem to suffer from cutters moving in the collet or the collet spinning in the spindle. I suspect that any R8 problems will be caused by insufficient tightening poor cutter shank size or condition or worn collet etc.

Mike

[Anonymous]

Posted by John Haine on 13/06/2020 09:53:14:

Someone posting here reckons that R8 drives perfectly fine without the peg.

The peg is intended to stop the arbor rotating while the drawbar is tightened. It provides no drive capability; that's due to friction on the taper. Both my R8 mills have no, or broken, pegs and they work fine.

Andrew

[old martParticipant @oldmart]

SOD, your illustration with the red highlights conveniently leaves out the top end of the R8. Why is that?

The point where the lack of diameter in the MT3 makes it more  flexible than R8 is where the tool emerges from the spindle.

Edited By old mart on 13/06/2020 13:53:53

[oldveloParticipant @oldvelo]

Jeremy Never be put off asking questions on this forum they are all fine just sometimes the answers are the silly part.

John Haine has summed it nicely. R 8 tooling for your mill with MT 3 Spindle it does not apply.

[old martParticipant @oldmart]

The op's question was answered immediately, but, as often happens on almost all forums, the subject matter has wandered in various directions. I am as guilty as anyone else.

[VicParticipant @vic]

Posted by Barrie Lever on 12/06/2020 18:19:34:

I have used INT30 and MT2 in the same machine and INT30 wins hands down and would win over MT3 as well.

What really matters is the cross sectional area once out of the spindle and INT30 is good in this area.

INT30 releases nicely and goes back in the same place (Z direction).

Emgee mentioned the EMCO specific INT30 tool holders, these were/are the best that you can get as they have pocket for the ER25 collet some what buried inside the tool holder giving more head room on a small machine and further increasing the stiffness.

MT direct collets work well and give more headroom and stiffness.

Machines with INT30

EMCO F1, Denford, Boxford, Wabeco and probably many more.

B.

They had a couple of small CNC mills where I used to work and the INT30 ER chucks were brilliant. Each machine had eight or ten for rapid changes. They also had linear guides and ball screws.

MT and R8 have their uses but for milling machines both are old out of date systems. If it wasn’t for hobbyists the R8 probably would have ceased to be used decades ago. Morse tapers on the other hand continue to be deemed useful for tailstock barrels on both MW and WW lathes.

I guess it’s much too expensive but it would be nice to see manual mills in hobbyist sizes with modern features.

[old martParticipant @oldmart]

INT30 is superior to R8, although the industry standard is INT40. My old firm used INT40 on all the CNC's and INT50 on the two biggest manual mills, the toolmakers had a couple of Bridgeports with R8.

 Vic, that mill you had with MT2 and INT30 sounds like a T S M1 to me, you will appreciate why I modified a light vertical spindle from MT2, to R8. Changing it to INT30 would have been too ambitious.

Edited By old mart on 13/06/2020 20:56:19

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[old martParticipant @oldmart]

I was just looking at the current South Bend milling machines and their biggest is the SB1028, a 10 X 54 Bridgeport style mill. I was surprised that this one has a 5hp motor, but still has the R8 spindle. I would have expected BT40 with that ammount of power.

[SillyOldDufferModerator @sillyoldduffer]

Posted by old mart on 13/06/2020 13:49:51:

SOD, your illustration with the red highlights conveniently leaves out the top end of the R8. Why is that?

The point where the lack of diameter in the MT3 makes it more flexible than R8 is where the tool emerges from the spindle.

…

Ah ha, I'm not explaining myself properly!

There are two different desirable features in a milling machine's tool fixing system:

1. It's ability to resist sideways bending, AND,
2. Being able to transmit torque to the cutting tool without slipping.

The top of the R8 is a parallel register and no doubt it improves stiffness. On that point R8 is better than MT3 because MT tapers are slimmer. But I didn't colour the register top because it contributes nothing to power transmission. ( I believe!)

It's point two that has me worried. The R8 taper has a small surface area compared with MT, and power handling depends on it, just like a clutch. As the amount of friction between taper and socket is proportional to contact area, taper angle and drawbar pull it seems likely to me that R8 can't transfer as many watts to the cutting edge as MT2 could without slipping. Unless R8 drawbar force is higher than applied to MT?

I thought the key-way explained the difference, but owners say the R8 key-way doesn't transfer power.

I'm not convinced MT tapers are much less stiff in practice than R8 either. On their own, maybe, but when cutting they're supported by the mill's spindle.

Couple of unanswered questions:

• Any evidence that MT tools bend?
• Any evidence that R8 tapers slip?

The answer to both in normal conditions is likely 'no'. If MT doesn't bend I suggest it's not worth paying extra for R8 on a small Chinese Mill, and if R8 doesn't slip it would be daft to replace it with MT on a Bridgeport!

Dave

[Martin ConnellyParticipant @martinconnelly55370]

You can put far more tension on the R8 draw bar than on a Morse taper one as it is not going to jam like a morse taper will. Since the ability to transmit torque is going to be a function of this tension as much as anything else then without a suitable formula taking into account area, angle and drawbar tension then area alone is not much of a guide (assuming coefficient of friction is the same for both systems. I'm going to look for one now.

Martin C

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