MT3 vs R8 spindle taper

[Eyecon]

You can also rig up a dial indicator and a 123 block to do the same. Feel free to PM if you need detailed help.

 

[jcdammeyer]

You can also rig up a dial indicator and a 123 block to do the same. Feel free to PM if you need detailed help.

Haven't received the tool setter yet. Supposed to arrive Jan 4th. I suspect it will be sooner but it's currently in limbo here which is code for it's now on a container on a boat headed your way...

Eventually I'll get a Canada Post email that a label has been created.

 

[Susquatch]

Sigh....sorry I have to write this....

OMG OMG no pin, pin broken, what am I to do????? Take it to a machinist to fix it.....W A I T!!! (Insert your won name here) I am a machinist, problem solved.

You guys so funny.

I must have missed something. I have no idea what is funny about us guys. I'm busy as an ant on a hot chocolate bar harvesting my corn right now!

I do agree with you though. The pin is not a big deal. I bought a small bag of 10 plain set screws and just turned two down to fit my mill spindle and the R8 collet slot. It was easy peasy to do and now I have a spare that I keep with my mill tools. I have not broken the new one since I put it in and I don't expect that I ever will.

Anyways, it looks like @Eyecon has decided to get an MT3 spindle so the lock screw doesn't matter anyway!

@Eyecon - after you get your MT3, make sure you don't leave a holder in the spindle for more than a week or so. I've had mine get stuck in my old mill/drill on me more than once that way. I think it's best to remove it after use. I've never had that problem with my R8 mill.

It's been a good discussion. Thanks for posting your question.

 

[Susquatch]

Feel free to PM if you need detailed help.

Personally, I'd much prefer that this type of discussion stayed on the main forum board rather than get lost in a PM. Its not personal or private. It's educational and informative. I think we all benefit from that. Those who don't care can just scroll down!

 

[jcdammeyer]

Do you have a dial or digital tool setter? The process would be to set the probe against the reference ground surfaces of the setter and then move the quill to and down on to the “plunger” of the setter until it reads zero. The tool setter is obviously zeroed relative to the reference ground surfaces(using a gage or 123 block) The difference between the machine absolute position when the probe triggered vs when the quill reached zero on the setter is the exact height of your probe trigger point relative to the quill(which is your WCS reference for tool heights and probe height in Z)

This is exactly what I ordered. https://www.aliexpress.com/item/1005003797600365.html
Looks like it can move 5mm from the 95mm height. At least if 'itinerary' is distance it can move. There's also an N/C overtravel switch which will be wired into the Z axis limit switch circuit.

I can bring the spindle down to a 1-2-3 block until it has friction clearance. Set Z to zero at that point and then move it over and bring it down on the tool sensor until it trips. A bit of math will tell me the height above the table that it will trip and it's supposed to be very repeatable so I can verify that too.

 

[Tom Kitta]

To answer original question. R8 exists for a reason - if MT3 was good enough they would use that - BUT R8 was designed for a much larger machine - for BP to work with transfer of power of max 3hp (or maybe 5hp). However, the machine to use MT3 is much smaller than even smallest BP - the MT3 spindles AFAIK are cheaper to make than R8 and thus seller should give small discount. Other than that there is not really that much difference, how much can the MT3 taper stick or move under power in a small mill vs. R8?
Note that if MT taper was "sticking" in the spindle it would not be used in a drill press where all force is down - certainly not in large drill presses with 5hp motors using MT5 - would not want that to stick

Bottom line is R8 is more specialized for milling collet than MT3 BUT for a small mill it may not really matter. I wonder what say Dabbler has to say about this - did anyone do comparison tests that we know of? I mean someone had to.

 

[Eyecon]

This is exactly what I ordered. https://www.aliexpress.com/item/1005003797600365.html
Looks like it can move 5mm from the 95mm height. At least if 'itinerary' is distance it can move. There's also an N/C overtravel switch which will be wired into the Z axis limit switch circuit.

I can bring the spindle down to a 1-2-3 block until it has friction clearance. Set Z to zero at that point and then move it over and bring it down on the tool sensor until it trips. A bit of math will tell me the height above the table that it will trip and it's supposed to be very repeatable so I can verify that too.

Yes absolutely that’s a good way to go as well…should get you within 20-40um/.001-.002”. I think a slightly safer approach with this method is to bring the spindle down lower than the block then raise until the block barely slides under it. The tool setter I was referring to for more accurate/repeatable measurement is a manual one, like one of these: https://a.co/d/3dTcuDD
Useful for measuring your probe and also verifying that things are working before trusting the tool table…even though i have a couple of cnc routers which are not particularly super accurate, this type of setter really helped me validate my setup before ruining relatively expensive stock materials.

 

[Eyecon]

To answer original question. R8 exists for a reason - if MT3 was good enough they would use that - BUT R8 was designed for a much larger machine - for BP to work with transfer of power of max 3hp (or maybe 5hp). However, the machine to use MT3 is much smaller than even smallest BP - the MT3 spindles AFAIK are cheaper to make than R8 and thus seller should give small discount. Other than that there is not really that much difference, how much can the MT3 taper stick or move under power in a small mill vs. R8?
Note that if MT taper was "sticking" in the spindle it would not be used in a drill press where all force is down - certainly not in large drill presses with 5hp motors using MT5 - would not want that to stick

Bottom line is R8 is more specialized for milling collet than MT3 BUT for a small mill it may not really matter. I wonder what say Dabbler has to say about this - did anyone do comparison tests that we know of? I mean someone had to.

Excellent points, and indeed the MT3 model is about 350 cad cheaper and is in stock vs the R8 which maybe hopefully will be in Canada in Feb. For the 350 I can get a decent starter TTS kit from Tormach including shipping or lots of cheaper Asian replicas to play around with. From what I read on UK and other European based forums, R8 is very rare there and folks over there seem to do just fine without it. I believe the popular Optimum bench top mill which is a bit bigger and heavier than the PM25 clone I’m getting uses MT4. Certainly in the world of VMCs you don’t see any of these older style machine tapers which is why I was lost and confused in making the decision. In any case, I don’t think MT3 is as rare here in Canada or the US especially with Asian imports.

 

[jcdammeyer]

Yes absolutely that’s a good way to go as well…should get you within 20-40um/.001-.002”. I think a slightly safer approach with this method is to bring the spindle down lower than the block then raise until the block barely slides under it. The tool setter I was referring to for more accurate/repeatable measurement is a manual one, like one of these: https://a.co/d/3dTcuDD
Useful for measuring your probe and also verifying that things are working before trusting the tool table…even though i have a couple of cnc routers which are not particularly super accurate, this type of setter really helped me validate my setup before ruining relatively expensive stock materials.

I wanted a tool sensor to be able to connect into LinuxCNC because I'm using both TTS and R8 tooling. Hence my trials and tribulations with my power draw bar. So I want the ability to place a tool into some kind of R8 holder and move over and determine the length of the tool without some sort of external measuring rig like sold by Tormach.

 

[Eyecon]

I wanted a tool sensor to be able to connect into LinuxCNC because I'm using both TTS and R8 tooling. Hence my trials and tribulations with my power draw bar. So I want the ability to place a tool into some kind of R8 holder and move over and determine the length of the tool without some sort of external measuring rig like sold by Tormach.

Yes if you measure the tool each time with the tool probe you are getting, knowing the probe height is irrelevant, all you need to determine is the offset between your WCS zero and the top of the sensor. I have this setup as well on one of the routers I use mainly for wood and composites because dimensional accuracy is not as critical.

 

[Eyecon]

Don’t get me wrong though, there are so many ways of doing this and from my experience they all get you to the same result.

 

[Susquatch]

Note that if MT taper was "sticking" in the spindle it would not be used in a drill press where all force is down - certainly not in large drill presses with 5hp motors using MT5 - would not want that to stick

I guess it depends on your definition of sticking. My mill drill is a big drill press. Then again, so is any mill. Lots of times used for vertical drilling.

It sticks (by my definition) all the time. On occasion after a lot of heavy drilling I have to literally pound on the drawbar. To the point that I added a heavy duty anvil to the top of the drawbar. I use a heavy brass hammer on it.

On the other hand, my R8 has never required more than a light tap with a plastic mallet.

I think that is the reason that they call the R8 a semi-self-releasing taper.

I should add that my mill/drill is an old girl. It has a 3/8 set screw built in to the spindle nose to help hold an installed taper provided that the taper has the corresponding flat for it.

 

[DavidR8]

Since the topic of sticking MT3 tapers I went out to see if mine was stuck. It's been tightened to working tension with a TTS holder since August. Undid the drawbar a few turns and rapped the drawbar with the end of the ratchet and out it came.

 

[Dabbler]

I've never been biased against MT3 - all my lathe tail stocks use it - but I have a slight preference for R8. But it isn't worth a lot of wait and uncertainty.

BTW I have had, in an exceptional circumstance, had an R8 stuck - I was stupid - but it came out OK when I realized my mistake.

My preference for R8: I have used 3/4 inch cutters in both. I think the alignment and holding is actually slightly better in R8, but that is a completely subjective thought. I seem to crank down on MT3 more on larger cutters. but hey - they both work.

 

[Susquatch]

Undid the drawbar a few turns and rapped the drawbar with the end of the ratchet and out it came.

You rapped your drawbar with a steel ratchet? I've always been told that was a big no-no. Might also explain why yours doesn't stick. So would oil.

 

[Six O Two]

I've had RF30 clones with MT3 and R8 tapers. My current mill has an r8 taper, even if my lathe has an MT3 tailstock. There wasn't a lot of tool overlap with the lathe when I had the milldrill with an MT3 taper as most of my lathe tools already had a tang instead of threads for a drawbar.

Like many others in this thread, I much prefer R8 for a mill. My tools used to get stuck in my mt3 milldrill all the time, and I often had to break out the drifts to get them out lest I fowl up the threads on the drawbar. That was a huge pain compared to R8 tooling.

R8 generally has easier/better re-sale as well in my experience.

 

[DavidR8]

You rapped your drawbar with a steel ratchet? I've always been told that was a big no-no. Might also explain why yours doesn't stick. So would oil.

Yup, I don't have a fancy hammer with a socket on it so I just rap it with the butt end of the ratchet handle.

 

[jcdammeyer]

Some rambling...

One of the principal issues with MT tooling is it doesn't handle lateral (side) forces very well. It's why you can have MT on the tail stock or spindle for centers and drill bits.

But try and mill with a cutter held in the drill press chuck and be prepared to wear it. Literally and perhaps internally. That's why a drawbar for MT tooling is mandatory!

Taper angle is 1.4377 theoretically for a length of 3.19". The small diameter is 0.7780" so let's just make it a cylinder rather than a cone to simplify the math. Pi x D x L is 7.7968 square inches. That's roughly the surface area in contact with the MT3 socket. If it's wedged in tightly making contact that's a lot of friction area. And because it's such a small angle a large distance is required before it's no longer touching or at least loose.

Now let's look at R8. The angle now is 8 degrees 25.5 minutes. Length of engagement is 0.94" and this angle is too steep to consider it a cylinder from 1.25" to 0.94".
Using this calculator:
https://keisan.casio.com/exec/system/1223372110
Surface area is 5.19 square inches. Doesn't seem that different.

However the angle and length of engagement is dramatically different; essential 1/3rd. And since the angle is steeper the distance between the collet and the spindle increases more rapidly and so releases faster and therefore more easily.

I believe because the angle is so shallow and over such a long length that unless the tapers are absolutely identical MT tapers don't contact completely until they are under a lot of force and then they sort of flex into contact making them harder to separate. Lateral vibration will in effect wiggle it loose.

Based on the testimonials most often MT3 drops out once the drawbar is loosened with only a light tap to shake it free. It's been many years since I pulled an MT3 holder into the drill press spindle. I don't remember having trouble releasing it.

I know I have to use the wedge and a hammer to release the pressed in Drill Chuck MT3 holder.

 

[Eyecon]

So a bit of bad news: it seems I was dealing with a bait and switch seller on eBay, after chasing them for the past couple of days to switch my order to the MT3 version they told me it’s not in stock and I have to wait until next February. I opened a dispute with eBay to get my money back. Looks like I’m going to end up getting an R8 mill after all
(I don’t ever do this but for reference seller is sumaiglobal42…things escalated really badly so leaving the name here because I wouldn’t want to see anyone go through this experience)

Now I’m looking for recommendations for something similar to the PM-25 work envelope (19x7) with a brushless motor and belt drive. Any suggestions?
I’ll contact PM tomorrow to inquire about shipping but open to other suggestions.

 

[YotaBota]

Yup, I don't have a fancy hammer with a socket on it so I just rap it with the butt end of the ratchet handle.

The right tool for the job! LOL
BTW - chisels make great screwdrivers. LOL