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krymis
01-04-2007, 10:24 AM
this message is pretty much directed towards bob, but also anyone wha can help. I wanted to know if anyone has removed the pin inside the r8 spindle. From the conversation on the iso30 spindle it seems that the pin can be removed without any ill effects. Is this true? I have the same power drawbar from joe that bob has, and put the extra clips and springs on it like bob's. I would like to know as this would expidite my prototype attempt at an atc.

BobWarfield
01-04-2007, 05:32 PM
Aaron has said somewhere you can pull the pin. That's good enough for me.

Apparently it is accessible if you extend the quill fully through a slot. That makes it easy to test. Pull the pin, insert your biggest nastiest cutter, set the deepest depth of cut you commonly would use, and see how it works before/after pin. Let us know.

Best,

BW

philbur
01-04-2007, 05:59 PM
Whether the tool will slip in the taper is primarily a function of how hard you pull on the draw bar versus how much torque you wish to transmit. The answer is almost for sure calculateable, at least to put you in the ball park, add 50% safety margin and you would be home and dry. Its looks like a relatively straight forward coefficient of friction calc.

Regards
Phil



this message is pretty much directed towards bob, but also anyone wha can help. I wanted to know if anyone has removed the pin inside the r8 spindle. From the conversation on the iso30 spindle it seems that the pin can be removed without any ill effects. Is this true? I have the same power drawbar from joe that bob has, and put the extra clips and springs on it like bob's. I would like to know as this would expidite my prototype attempt at an atc.

krymis
01-04-2007, 07:41 PM
this is exactly what i needed to hear. now i just need to set everthing up to get this done. At the moment i have my mill torn apart back to bare bones trying to tidy my conversion back up.

krymis
01-04-2007, 07:45 PM
bob,

what size support rods did you use for your PDR? I used .500 for mine and my springs were not as big or long as the ones you used. Do you think this will last? I am kinda concerned about that part....Where did you get your springs too?

philbur
01-05-2007, 09:45 AM
Here is a typical calculation. What is intersting is that if you half the speed but still want to transmit full HP then the draw bar tension needs to double. So overall it looks OK for 2 hp as long as you have a draw bar tension of around 1000 lbs and don't go below 200 rpm.

Cone Clutch Calculation for a R8 Taper from (Machinerys Handbook)

large radius of R8 taper r1 1.25 inches
small radius of R8 taper r2 1 inches
half R8 taper included angle a 8.425 degrees
coefficient of friction f 0.7
horse power H.P. 2 hp
spindle speed N 200 rpm
safety factor S 1.5


mean R8 taper radius r 1.125 inches
min. draw bar force Ps 1007.2 lbs

Regards
Phil


this is exactly what i needed to hear. now i just need to set everthing up to get this done. At the moment i have my mill torn apart back to bare bones trying to tidy my conversion back up.

BobWarfield
01-05-2007, 10:02 AM
bob,

what size support rods did you use for your PDR? I used .500 for mine and my springs were not as big or long as the ones you used. Do you think this will last? I am kinda concerned about that part....Where did you get your springs too?


Yeah, they are about 1/2". BTW, Vince on these boards (N4NV or some such name) has a Bridgeport he converted and he just built the same drawbar. Looks like he got his to work without return springs, so he musta had a stronger cylinder spring. He's got a post over on the Bridgeport section with a nice movie. Like me, he couldn't resist cycling a tool in and out when he first got the thing working. I was using mine this weekend and it was heaven. Anyone reading this needs to get a set of plans if you don't already have this gadget!

I bought my springs at Ace Hardware. Just grabbed the first thing that looked close. You have to adjust the tension by moving the collars up or down so the is enough force, but not so much the cylinder has trouble engaging smoothly. Frankly, I would have been happier to get mine to go without the springs. I keep pondering a mod to have those rods slide in some UHMW plastic bushings for better performance, but haven't done anything on it.

Krymis, I don't know why yours wouldn't last pretty well. These are not actually high duty devices. Even if you go CNC an ATC, I can't imagine you'd wear it out that fast. Might consider an inline oiler for your impact wrench if you plan to work it hard, though.

FWIW, I have a 3" diameter 7-insert Lovejoy facemill (expensive, but I got a great FleaBay deal and love the cutter) that is my heaviest cutter. Incidentally, it cuts well on the IH mill and leaves as nice a finish as my flycutter did but with much less noise and much faster. I suspect I can do even better if I get some coolant and really dial in optimal feeds and speeds. Anyway, it is good to know the mill is rigid enough to run this cutter on steel, but if I decide to pull my pin, I think this would make a good test.

Philbur, good calculation. We'll want to consider whether there might be a little oil that affects the Cf. I know my stuff has a little Break-Free on it to fight rust--live near the ocean. Certainly explains why the retention knob world uses such a big stack of Belleville washers to hold onto their toolholders. FWIW, there is a company making an R8 change system that claims 600lbs of springing is sufficient on R8. That's close enough to you number of 1000 to make sense. They just thread retention knobs into R8 collets and mill holders. Interesting approach. Don't know that I would prefer it over the power threaded drawbar though. Their system sure is expensive.

Best,

BW

pstockley
01-05-2007, 11:01 AM
From my experience, drilling (especially large diameter drills) will be the real test.

krymis
01-05-2007, 11:27 AM
thanks guys good to know where everything stands.
anymore info on this subject would be great.

philbur
01-05-2007, 03:06 PM
I think this is an interesting point.

Providing you are driving the drill into the work-piece the resistance to slipping in the spindle taper is self-compensating due to the increased force pushing the tapers together. However if you slack off for even a fraction of a second (as in pecking, or just to allow the chips to clear for example) then the tendency will be for the partially formed chip to pull the drill out of the spindle. This will have a tendency to relieve the force holding the tapers together and possibly allow the tool-holder to rotate in the spindle. A clear example of this is the problem with large tapered shank drills in the tail-stock of a lathe.

If you use spring washers with an air actuator and stud arrangement for tool release then your retaining force is limited to the spring washer force which is constrained by your desire not to damage you spindle bearings during activation (unless you are very clever with the design). If you use an air wrench solution then the draw bar tension is only limited by the strength of the draw-bar and the power of the wrench.

So if you really want to make a R8 ATC (a dubious proposition at best) without a drive key then the air wrench solution would appear to be the better solution. If you just want quick-change capability then leaving the drive key in place would probalby be a safer option, either with the spring washer or the air wrench arrangement. Personally I don't think that lining up the keyway is that bigger deal for a manual quick-change solution. Alternatively a damaged spindle taper could reduce you to tears, and I hate to see a grown man cry.

Regards
Phil



From my experience, drilling (especially large diameter drills) will be the real test.

philbur
01-05-2007, 03:56 PM
Another interesting modification to the air wrench design might be to include a thrust ball bearing between the underside of the drawbar nut and the top of the spindle. A 51101 looks suitable - 15mm ID and 28 mm OD - max static load 3000 lbs. This would ensure that more of the applied torgue finds its way down to the tool holder.

Regards
Phil


I think this is an interesting point.

Providing you are driving the drill into the work-piece the resistance to slipping in the spindle taper is self-compensating due to the increased force pushing the tapers together. However if you slack off for even a fraction of a second (as in pecking, or just to allow the chips to clear for example) then the tendency will be for the partially formed chip to pull the drill out of the spindle. This will have a tendency to relieve the force holding the tapers together and possibly allow the tool-holder to rotate in the spindle. A clear example of this is the problem with large tapered shank drills in the tail-stock of a lathe.

If you use spring washers with an air actuator and stud arrangement for tool release then your retaining force is limited to the spring washer force which is constrained by your desire not to damage you spindle bearings during activation (unless you are very clever with the design). If you use an air wrench solution then the draw bar tension is only limited by the strength of the draw-bar and the power of the wrench.

So if you really want to make a R8 ATC (a dubious proposition at best) without a drive key then the air wrench solution would appear to be the better solution. If you just want quick-change capability then leaving the drive key in place would probalby be a safer option, either with the spring washer or the air wrench arrangement. Personally I don't think that lining up the keyway is that bigger deal for a manual quick-change solution. Alternatively a damaged spindle taper could reduce you to tears, and I hate to see a grown man cry.

Regards
Phil

BobWarfield
01-05-2007, 04:34 PM
Interesting thing about drills if they are the worst case:

There's no drive pin in the Taper to Chuck interface. Sure looks like similar or less surface area too.

In the end, it is easy to just try it out on the IH rather than spend hours wondering.

Best,

BW

philbur
01-05-2007, 06:52 PM
But possibly much more expensive if the alternative is that you destroy the spindle taper due to an inappropriate design. Experimental engineering without realistic expectations can be a very expensive hobby, especially with a reworked spindle with high quality bearings. A little bit of theoretical engineering can save you many $$$$$.

A phrase that once again comes to mind is:

An engineer is somebody that can do for a penny what any fool can do for a pound.

It seems we have a fundamental difference in our approach to engineering. However it is clear to me that that my approach is right and therefore yours must be wrong.:boxing:

Best Regards
Phil





In the end, it is easy to just try it out on the IH rather than spend hours wondering.

Best,

BW

1990notch
01-05-2007, 07:32 PM
krymis,

My pin apparently baccked out on it's own to the point where it didn't engage the collet at all. I decided to remove it totally so it couldn't cause a problem. I didn't realize how easy it was until I did it though.

Here's how I did it: Lower the quill most of the way. Then looking through the slot in the quill, rotate the spindle by hand until the "pin" (it's just a set screw) lines up with the slot. Then using a small precision screwdriver, turn the screw inwards until it drops through the spindle where the collet's go. Took me 45 seconds to do it.

I haven't had any problems with it out yet. I'll post if/when I do.

BobWarfield
01-05-2007, 08:31 PM
It seems we have a fundamental difference in our approach to engineering. However it is clear to me that that my approach is right and therefore yours must be wrong.:boxing:

Best Regards
Phil

Philbur, I never doubted that would be your position and I thank you for your thoughtful lecture.

There are also those engineers who over engineer and over analyze. I run large engineering organizations for a living, and have to do so efficiently. I have some phrases of my own that I pass along to those who tend to over analyze when a simple experiment would do: Why reinvent the wheel? Or, to be more on point, why re-engineer or re-analyze that wheel? I have another engineer friend who is fond of pointing out when things are being over analyzed and a simple experiment would deliver the answer that the answer was "tragically knowable."

There are people such as 1990notch whose pins have fallen out who have run with them without ill effect that have posted on these and other boards. We have the example I presented of drill tapers, which use no such pins. There is Aaron telling us to go ahead, who has more experience than anyone with IH mills.

Let us know how your continued analysis comes out. Try to remember, models without supporting empirical data are often unproductive. Or, perhaps the example of chicken little is another illustrative case to consider.

Best,

BW

philbur
01-06-2007, 05:02 AM
Ooops:

http://www.galileo.org/schools/standard/bridges/index.html

Regards
Phil

QUOTE=BobWarfield;238564]
There are also those engineers who over engineer and over analyze. I run large engineering organizations for a living, and have to do so efficiently. I have some phrases of my own that I pass along to those who tend to over analyze when a simple experiment would do: Why reinvent the wheel? Or, to be more on point, why re-engineer or re-analyze that wheel? I have another engineer friend who is fond of pointing out when things are being over analyzed and a simple experiment would deliver the answer that the answer was "tragically knowable."

BW[/QUOTE]

BobWarfield
01-06-2007, 11:27 AM
Thank you for bringing up the Tacoma Narrows Bridge, Phil, as it is an excellent illustration of what I'm trying to convey about the importance of real empirical data and not just mathematics in engineering.

The original Tacoma Narrows design was reviewed and revised by the same man who designed the Golden Gate bridge, Leon Moisseiff. He designed or collaborated on many other designs at the time, and was considered the leading suspension bridge designer of his day. All of these bridges were designed using the same math that had always worked before.

Unfortunately, in the Tacoma Narrows case, they discovered a new phenomenon that had not been seen before and was not covered in their textbook mathematics of the time. There was no error in Moisheff's calculations, the mathematical models of the day just didn't account for the full physics of what happened because they weren't known. Moisheff had been designing bridges for 20 years at this point.

It is interesting to note that the disasterous oscillations resulting in the bridge's demise were easily detected even during construction of the bridge:

http://www.nwrain.com/~newtsuit/recoveries/narrows/gg.htm

The bridge was in fact nicknamed "Galloping Gertie" because of these oscillations long before it collapsed. The bridge was in use for four months with oscillations so bad that people of the day made a sport of watching cars appear and disappear as the bridge rocked up and down. As the article notes, several means of strengthening the bridge against these oscillations were tried to no avail.

This was not a case of "under engineering" or going off half cocked, it was a case that the engineering science of the day didn't understand or account for the phenomenon at all. As your link concludes, Phil:

"this bridge disaster still has people talking, well arguing really, as physicists and mathematicians argue about the true reason that the bridge collapsed."

A little more ability to gather and act on experimental data and a little less over confidence in the mathematical models and reputations of the engineers involved safe and sound in their offices might have prevented the disaster.

Pull the pin, watch what happens, if your bridge starts to oscillate, put it back. Phil, you leave your pin in. You've got more engineering calculations to do before you're ready to pull it.

Sincerely,

BW

Cruiser
01-06-2007, 12:39 PM
I think the true question regarding the r-8 stop pin is going to be an in use question, There is an "IF" involved, as in our shop with numerous bridgport mills, they occasionally get damaged and sheared off ! If it gets sheared off from a torque application then you can end up with a problem, So, If you remove the pin and have a similar problem, what will be the result ? A spun r-8 holder or collet will cause a lot of friction and pressure that can create for you a general use beater spindle, we have two machines in this catagory now and spindle replacement is not being concidered. It is a fact that with the air drive on the draw bar that the pin will at times be in the way, and that for general light use it is not needed, but it is there for the ocasional high torque needed for some slight reassurance, but without garantee, that your holder won't spin anyway ! Or will it ? A gauled taper, or bell'd out taper will not have the same hold as a good taper and then the sloap gets steaper and the snowball goes faster. So, I conclude my two cents worth with " IF you get away with it" ...........

philbur
01-06-2007, 01:33 PM
An interesting point of view and a nice try, but it dances around the basic issue, which of course is the failure to take into account all of the forces involved. Everything else is merely about apportioning the blame. Was the design over or under analysed?

The Challenger space shuttle disaster is an interesting example of managements desire for efficiency (maintaining schedule) that appears to have over-ruled the engineering analysis, with disastrous consequences.

The seven P's comes to mind: Proper Prior Planning Prevents Piss Poor Performance.

Regards
Phil



Thank you for bringing up the Tacoma Narrows Bridge, Phil, as it is an excellent illustration of what I'm trying to convey about the importance of real empirical data and not just mathematics in engineering.

The original Tacoma Narrows design was reviewed and revised by the same man who designed the Golden Gate bridge, Leon Moisseiff. He designed or collaborated on many other designs at the time, and was considered the leading suspension bridge designer of his day. All of these bridges were designed using the same math that had always worked before.

Unfortunately, in the Tacoma Narrows case, they discovered a new phenomenon that had not been seen before and was not covered in their textbook mathematics of the time. There was no error in Moisheff's calculations, the mathematical models of the day just didn't account for the full physics of what happened because they weren't known. Moisheff had been designing bridges for 20 years at this point.

It is interesting to note that the disasterous oscillations resulting in the bridge's demise were easily detected even during construction of the bridge:

http://www.nwrain.com/~newtsuit/recoveries/narrows/gg.htm

The bridge was in fact nicknamed "Galloping Gertie" because of these oscillations long before it collapsed. The bridge was in use for four months with oscillations so bad that people of the day made a sport of watching cars appear and disappear as the bridge rocked up and down. As the article notes, several means of strengthening the bridge against these oscillations were tried to no avail.

This was not a case of "under engineering" or going off half cocked, it was a case that the engineering science of the day didn't understand or account for the phenomenon at all. As your link concludes, Phil:

"this bridge disaster still has people talking, well arguing really, as physicists and mathematicians argue about the true reason that the bridge collapsed."

A little more ability to gather and act on experimental data and a little less over confidence in the mathematical models and reputations of the engineers involved safe and sound in their offices might have prevented the disaster.

Pull the pin, watch what happens, if your bridge starts to oscillate, put it back. Phil, you leave your pin in. You've got more engineering calculations to do before you're ready to pull it.

Sincerely,

BW

krymis
01-06-2007, 07:23 PM
guys please stand down and lets talk and act. I removed the pin from my seig mill and now i need to know what test to do to see if it will work. the seig mill is a good starting point as the spindle can be replaced for a few dollars. This will give us a good starting point and then we can move on the ih mills. also i would lean towards removing the pin if arron has metioned removing it. If he has mentioned it then he 99% surely has done it. if it was good for him then it may be good for us. Tell me what test to run with what cutters and i will do them and post back. I feel the atc in r8 form can be accomplished but there has to be a reason why noone has done it. We need to ask gene if he did in fact get the design drawings and such from arron for his atc. For those of you who did not know arron has been working on one.

Runner4404spd
01-06-2007, 09:27 PM
i think the problem with the seig mill is that you won't be able to use a cutter large enough for this to really be a problem. when you say seig i'm thinking mini mill. if i'm wrong please correct me. however, the size of the cutter that can be used with the IH is enormous. just today, i was taking 7/8 wide cuts in aluminum that were .300 deep, but then i'm running at 3200 RPM as opposed to the stock 1600.

BobWarfield
01-07-2007, 12:32 AM
also i would lean towards removing the pin if arron has metioned removing it. If he has mentioned it then he 99% surely has done it. if it was good for him then it may be good for us.

Krymis, take a look at post #73 in the ISO spindle thread:

"Take the R8 pin out, it makes tool changes a lot faster."


An interesting point of view and a nice try, but it dances around the basic issue, which of course is the failure to take into account all of the forces involved. Everything else is merely about apportioning the blame. Was the design over or under analysed?


No dancing involved there at all. It's very clear cut. Philbur, I'll leave you to your trolling at this point. Keep your pin in, it suits.


but it is there for the ocasional high torque needed for some slight reassurance, but without garantee, that your holder won't spin anyway

Cruiser, on this we absolutely agree. There will be a level of torque where you'll likely risk spinning the holder and damaging the taper. One wonders how much horsepower that takes, what sort of cutter, and how fast it happens.

Sincerely,

BW

Cruiser
01-07-2007, 01:21 AM
Krymis, take a look at post #73 in the ISO spindle thread:
Cruiser, on this we absolutely agree. There will be a level of torque where you'll likely risk spinning the holder and damaging the taper. One wonders how much horsepower that takes, what sort of cutter, and how fast it happens.

Sincerely,

BW

simple ...... just enough ....... instantanious !

philbur
01-07-2007, 07:16 AM
The risk of spinning the taper comes from high torque, which will be at its highest for a geared head mill, such as an IH, running at its lowest rpm. An interesting point is that machines with VFD's and other electronic drives will be at less, and possibly no risk, as they generally do not generate higher torque at lower rpms, whereas a mechanical gearbox is basically a torque multiplier.

So the best "test to destruction" would be an IH running at its lowest rpm with its largest diameter cutter on steel. Wind up the depth of cut/feedrate until the motor complains or the taper slips.

How about it Bob, it's a simple test and then you will have your empirical data.

Regards
Phil



i think the problem with the seig mill is that you won't be able to use a cutter large enough for this to really be a problem. when you say seig i'm thinking mini mill. if i'm wrong please correct me. however, the size of the cutter that can be used with the IH is enormous. just today, i was taking 7/8 wide cuts in aluminum that were .300 deep, but then i'm running at 3200 RPM as opposed to the stock 1600.

krymis
01-07-2007, 09:44 AM
ok so if i do this test on the ih mill what will happen that will really piss me off? Is this the point were i will ruin the spindle? I mean does it really depend on the cutter i'm using? The speed i am using it at? and the material i am cutting?

Cruiser
01-07-2007, 10:34 AM
Krymis, The real truth to the point is that it can happen even if you leave the pin in place ! A simple thing like your program loosing your tool offset and your machine crashing into stock or vice or table or whatever is in way with enough built up energy can read "CAN" do some damage or lots of damage other than the cutter against the impact zone. Its like slipping on a bar of soap ! as far as damage to the taper in spindle, it would also depend on any and all possible non perfect conditions at that point too. As far as the test goes lets be diplomatic about it and take a vote ! My vote is to approve B.W. testing the full range of possibles and fileing a report here for all to read ! That way will be fair and just !

Geof
01-07-2007, 11:35 AM
The purpose of the pin in the R8 taper is to stop the collet spinning when the drawbolt is run into the thread in the collet; the drive for the cutter is taken by friction on a correctly tightened collet.

Consider two situations:

1) The cutter in the collet is driven solely by friction; there are no pins or keys just a smooth round shank in a smooth round hole. When the frictional grip is tight enough to drive the cutter it is more than tight enough to drive at the taper which is transmitting the same torque at a larger radius, i.e. longer effective lever.

2) The pin size, less than 3/16" diameter, is totally inadequate to transmit the forces involved in driving a R8 shank mounting a large diameter face mill at something like 100 rpm through the belt and back gear reduction from a 2 HP motor. If the drawbolt is not tight enough to transmit the drive by friction the pin will simply shear off under a decent cut.

Also consider that ER, and other collets whether double or single angle, drive solely by friction and there is a myriad of lathe collet chucks that drive solely by friction.

BobWarfield
01-07-2007, 11:40 AM
Probably should test my spindle to failure as well, eh, Cruiser? Then we'd know where the limit was. LOL

Krymis, you're just going to have to decide on your own. You've got Aaron's input. There've been others here who've run without a pin. You can amble over to Practical Machinist and find more. There's fellas over there who fuss and argue about it too, with a contingent saying their fastest machinists pull the pin and another contingent saying terrible things can happen.

You can also play it safe and leave the pin in. In the end of the day, any modification you make to your machine sorta leaves you having to decide. They can all lead to disaster of one kind or another, and CNC itself has the potential to do as much or more damage as most other things you could do. Cruiser's example of a machine crash into stock, table, vise, rotab, etc. is on point for that. And BTW, all these machines large and small have tremendous potential for personal injury as well.

If you are really thinking about pin pulling for automatic toolchanger purposes, did you get an ISO 30 spindle from Aaron's sale? That taper is ultimately better suited. BTW, there will be the equivalanet pin-pulling forelock tugging and hand wringing exercise with the ISO spindle as well. Drumroll please:

Do you have to put those two ears on and wind up having to index the spindle to their location or can you get by without them?

Hmmm, well if you run 'em without the ears and have a crash you can spin the holder and ruin your spindle, yada, yada, yada.

BW

philbur
01-07-2007, 02:27 PM
I think you are of course correct in that the R8 key is primarily there to prevent rotation during installation and removal. However in marginal torque situations the resistance to slipping will be a function of the sum of the resistance due to friction of the taper itself plus the resistance to shear of the key.

The maximum size of cutter you should be mounting in a R8 collet is 3/4". In this case the applied torque due to say a 2 hp motor through a gear box is limited by the fact that you will be running the cutter at something like 450 rpm or greater when cutting steel. The real issue is large diameter cutters, say 2" to 3", mounted in a R8 toolholder running at say 150 rpm. In the later case the applied torque will be 3 times that of the the former.

I agree also regarding the myriad of collets driving on friction only. However there is a point where they run out of steam with respect to transmitted torque. Hence the beefy drive dogs on an ISO30 tool holder together with a weldon type cutter.

This is all interesting stuff but we should all try not to get to serious.:)

Regards
Phil




The purpose of the pin in the R8 taper is to stop the collet spinning when the drawbolt is run into the thread in the collet; the drive for the cutter is taken by friction on a correctly tightened collet.

Consider two situations:

1) The cutter in the collet is driven solely by friction; there are no pins or keys just a smooth round shank in a smooth round hole. When the frictional grip is tight enough to drive the cutter it is more than tight enough to drive at the taper which is transmitting the same torque at a larger radius, i.e. longer effective lever.

2) The pin size, less than 3/16" diameter, is totally inadequate to transmit the forces involved in driving a R8 shank mounting a large diameter face mill at something like 100 rpm through the belt and back gear reduction from a 2 HP motor. If the drawbolt is not tight enough to transmit the drive by friction the pin will simply shear off under a decent cut.

Also consider that ER, and other collets whether double or single angle, drive solely by friction and there is a myriad of lathe collet chucks that drive solely by friction.

Geof
01-07-2007, 02:45 PM
....This is all interesting stuff but we should all try not to get to serious....Phil

I disagree. The people on this forum range from the DIY/hobbyist all the way through novices intending to make a career in machine work up to people who make or have made their living in machine work. As one of the latter I find it very frustrating when I encounter novices, and sometimes even so-called journeymen, who have wrong ideas and are incapable of analysing how mechanical devices function.

Your comparison between the R8 collet and the ISO30 with a weldon type cutter is irrelevant to the topic of what the function of the pin is in the R8 taper; these are two totally different designs with totally different functions.

philbur
01-07-2007, 03:26 PM
To answer your questions directly

1) You may damage your spindle.
2) Yes.
3) not necessarily.
4) Yes.
5) not necessarily.

The main point with a gear head or direct belt drive type mill is that the AC induction motor runs at constant speed and has the ability to apply its full horse power, regardless of what you are cutting, what speed you are doing it at and what cutter you are using. The gear box/belts transmits all of that horse power (less any frictional losses etc). So if the gearbox/belts reduce the motor rpm from 1700 to 170 rpm the horse power at the cutting tool is still the same as the motor (say 2 hp) however the maximum available torque (twisting force) is now 10 times what it was at the motor. So if you jam the cutting tool into the workpiece hard enough one of four things will happen.

1) You break the cutting tool.
2) You tool holder will slip in the spindle taper.
3) You stall the motor or have belt slip.
4) Something else in the drive train breaks.

At higher rpms point 3) becomes more likely than points 1), 2) or 4). At lower rpms, when you are most probably using big strong cutters then point 2) or 4) become more likely. Both of which are of course bad news.

If you are cutting aluminium then your rpms will be relatively high so again 3) is more likely. If you are cutting steel then rpms are lower so 1), 2) or 4) are more likely.

Regards
Phil



ok so if i do this test on the ih mill what will happen that will really piss me off? Is this the point were i will ruin the spindle? I mean does it really depend on the cutter i'm using? The speed i am using it at? and the material i am cutting?

philbur
01-07-2007, 03:35 PM
We seem to agreed about the function of the pin on the R8 and that the function of the drive dogs on an ISO30 is different!!!!

I apologise if my post has in some way upset you, it was not my intention

Regards
Phil



I .....is irrelevant to the topic of what the function of the pin is in the R8 taper; these are two totally different designs with totally different functions.

Geof
01-07-2007, 04:13 PM
ok so if i do this test on the ih mill what will happen that will really piss me off? Is this the point were i will ruin the spindle? I mean does it really depend on the cutter i'm using? The speed i am using it at? and the material i am cutting?

If you are using a helical cutter in a collet and it is not tight enough the screwing action under cut will pull the tool out of the collet; your chance of having the collet spin in the taper is practically zero.

If you are using a shank holder with a large weldon type cutter or a face mill and it is not tight enough you have a good chance of spinning the holder in the spindle taper. However, as a mention previously, if you have a large cutter and are transmitting a reasonable amount of torque the pin will probably shear anyway because it is simply too small to transmit cutting torque.

The bottom line is tighten the drawbolt sufficient to pull the collet/shank into the taper tight enough that the frictional grip is more than adequate to transmit the working torque.

philbur
01-07-2007, 05:33 PM
Hi Geof,

Again I agree with what you say but the nub of the issue is what is the limit on working torque of an R8 taper before it slips. Surely there is one, and more specifically the IH mill is possibly capable of delivering it. I think you will agree that tool slippage under heavy load is not an infrequent problem and that the possibility and consequences should not be dismissed to lightly.

Best Regards
Phil




The bottom line is tighten the drawbolt sufficient to pull the collet/shank into the taper tight enough that the frictional grip is more than adequate to transmit the working torque.

Geof
01-07-2007, 05:53 PM
Hi Geof,

Again I agree with what you say but the nub of the issue is what is the limit on working torque of an R8 taper before it slips. Surely there is one, and more specifically the IH mill is possibly capable of delivering it. I think you will agree that tool slippage under heavy load is not an infrequent problem and that the possibility and consequences should not be dismissed to lightly.

Best Regards
Phil

Having used a R8 taper with a 3" face mill driven by a 5hp motor taking cuts heavy renough to load the motor down in a spindle without a pin without the shank slipping in the taper I am confident an IH mill will never be able to make it slip if the drawbolt is tightened correctly.

Tool slippage inside the collet, the unscrewing effect I mention, is common. Shank slippage inside the taper I have not encountered.

philbur
01-07-2007, 07:22 PM
Well if you had shared this experience with us earlier it might have save a great deal of discussion. Cruiser in post 18 however appears to have a different experience. My own understanding was that an R8 is generally recognised to be running out of reliablilty at about 3 hp, assuming everything is in A1 shape.

Thanks anyway.

Best Regards
Phil


Having used a R8 taper with a 3" face mill driven by a 5hp motor taking cuts heavy renough to load the motor down in a spindle without a pin without the shank slipping in the taper I am confident an IH mill will never be able to make it slip if the drawbolt is tightened correctly.

Tool slippage inside the collet, the unscrewing effect I mention, is common. Shank slippage inside the taper I have not encountered.

Cruiser
01-08-2007, 06:57 AM
Lets put it this way, more than likely you can do anything you want to do using std practices without the pin and nothing will happen BUTT stuff happens !

krymis
01-08-2007, 08:42 AM
so i have the mill table all put back together and will be working on the rest next week. This week too i guess. While putting it back together I will pull the pin. After that i will be testing it. I use nothing bigger than a 1" end mill for almost all my stuff. So think i should be fine. However, you will see a post of the outcome and so on.