keeping the spindle from hitting the table

[devincox]

I have my x and y done and have started on the z axis and man these ball screws move freely!

What are you guys with ballscrew conversions using to keep the z axis from hitting the table if the power suddenly goes out?
I have seen some guys using counter balances but some complain the counter balance can introduce backlash.
Someone posted up a part # for an electromagnetic brake, but I can't seem to find that post anymore.

What does the IH CNC Kit use?
Do the servos + pulley gearing slow it up enough?

Thanks,
Devin

[Cruiser]

TIGHTEN THE GIB !
It won't fall if the gib is tight enough to hold it in place. It is not supposed to be so loose it can gravitate. So
TIGHTEN THE GIB !

[devincox]

I had planned on tightening it up quite a bit, especially since I have the one shot oiling system and the oil grooves cut. It's just that head is sooooo heavy and the new ground ballscrews so smooth, I'm worried about ruining a part/table if the power goes out while I'm working.

Thanks,
Devin

[Cruiser]

The Gib along with the load of the drive mechanics should hold you in place. Mine does not want to drop at all, I don't even think about it anymore. Just adjust your Gib till it holds in position. Don't get into using the side grubs, they can distort the Gib, especially if they use the dog point grub and steel ball like mine had. I took mine out and they stay out. I found that mine had deep dimples and an interfering ridge around the dimples, Also I could see pressure rub zones on opposite side of grub. If you have hard plastic plugs under the grub then you can snub them a bit. Primarily tho, use the Gib as it is intended. That way the friction is evenly distributed along full Gib and it will hold better and slide smoother for its full life span.

[devincox]

thank you for your help.

Devin

[pete from TN]

This is an interesting question for me as I am nearly done with my Lathemaster cnc conversion. In this I have seriously lightened the millhead assembly and have a 3-1 ratio on the Z axis motor. I tighened my gibs snug and find that while it does not drop down, it would not take much for it to do so. I also do not use the lock screws to tighten the gib unless I am locking the head in position. I was seriously looking at getting an electric brake for the Z motor but you feel that you do not need one? I also understand that you had a system to help aid the lifting of the millhead with some pulleys or something. Do you feel that this is the reason you are able to just tighten the gibs and be able to keep the head from falling?

I was thinking that I might be able to just lock the gib locks when the machine is not in use and unlock them just before turning on the control unit so that the servos will lock. Only thing is you can't forget and run the machine with the gibs locked or damage will result. What are your thoughts on this method? peace

[Cruiser]

Pete,
My gearbox is lightened up too, I did a belt drive and put rails on the side of column, but nothing to assist in lifting or hold. As stated above I will not ever again use the side grubs on a Gib NEVER ! I have and then removed my Gib's to find the damage and localized wear patterns on them and didn't like it. My machine is NOT one of the nicely ground machines, It is a lapped in machine and needed break-in cycling to finish smoothing things out. With a 3 to 1 ratio you must be going for speed. If I remember correctly mine is 5 to 1 and 5 pitch ball nut/screw. My head will not fall, period. I've had instances where I lost power in a move and it would slide maybe 3 inches and stop, from a full rapid. My slide ways are pretty well broken in now too, so they are not near as sticky as they once were. I do not fully believe in a counter balance system or gas struts, I admit they can help in some machines but I don't need them, again, period.
I looked at the potential of adding a brake unit to assist the holding, but again, if it is adjusted properly, and the drives are tuned properly, and the Accel/decel are set appropriately, It would be a redundancy ! Not to mention the head ache of getting the signal to time in so the drive never felt it ! My IH system is working pretty good, My changes made were for my necessities, stemming from cast iron fine damage to the innards of the gear box, OF WHICH, Gene says this is never going to be an issue again ! My machine was purchased from Aaron about a year or so before Gene and Tommy took over things. Mine was an early version 3 pre grind or an 8" square. As for your thing, it is after all your thing ! OH, and how about pulling your Z Gib and look at the area where those grubs attack the Gib and report about the dimpling and wear patterning ? I be just barely curious ! but only a wee skoche ! ha ha ha and any questions, I usually answer them especially if I am asked.
Later Pete

[pete from TN]

Pete,
My gearbox is lightened up too, I did a belt drive and put rails on the side of column

I also recently completed a Belt drive conversion and that is the majority of the weight savings....



(With a 3 to 1 ratio you must be going for speed. If I remember correctly mine is 5 to 1 and 5 pitch ball nut/screw. My head will not fall, period. )


I was not going for speed at all really just did some computations with some help from others on here and arrived at either a three to one or four to one and with the available pulleys and sizes I was able to find this was the best combination. I am using some 1150 oz inch servomotors...




(I've had instances where I lost power in a move and it would slide maybe 3 inches and stop, from a full rapid.)

As I said my setup currently will hold it's position and that is without counterweight or power applied to the motors. I was only posting here to make the poster understand that your machine is not stock and his stock machine may not exhibit the same results... and to get your thoughts on an issue that affects anyone that attempts to convert their Z axis to cnc.



( My slide ways are pretty well broken in now too, so they are not near as sticky as they once were. I do not fully believe in a counter balance system or gas struts, I admit they can help in some machines but I don't need them, again, period.)

My apologies I thought it was your machine I saw with the pulleys and weight attatched to the back but I guess it must have been someone else....



(I looked at the potential of adding a brake unit to assist the holding, but again, if it is adjusted properly, and the drives are tuned properly, and the Accel/decel are set appropriately, It would be a redundancy ! Not to mention the head ache of getting the signal to time in so the drive never felt it !)

I understand that most of these brakes work by using some small amount of voltage to unlock the brake taken from the servo and basically it is instantaneous when the power is killed to the motor the brake applies.. My thoughts are that the state of tune of your drives and accel settings are irrelevant because the only time the head falling is an issue is when the power is off and the servos are no longer under the control of the cnc system.



(My IH system is working pretty good, My changes made were for my necessities, stemming from cast iron fine damage to the innards of the gear box, OF WHICH, Gene says this is never going to be an issue again ! My machine was purchased from Aaron about a year or so before Gene and Tommy took over things. Mine was an early version 3 pre grind or an 8" square. As for your thing, it is after all your thing ! OH, and how about pulling your Z Gib and look at the area where those grubs attack the Gib and report about the dimpling and wear patterning ? I be just barely curious ! but only a wee skoche ! ha ha ha and any questions, I usually answer them especially if I am asked.
Later Pete)



I am quite aware of your system working well which is mostly why I choose to ask you questions like this. My Z axis gibs have been out of the machine along with about every part in the machine for several months now and I have closely inspected and been over every inch of this machine during the cnc retrofit and noticed none of the damage you are talking about. My machine is nearly eight years old now and has more than it's share of break in and wear of the gibs. It was not a ground machine either. I am not quite sure what you mean by " your thing" I am hoping that it was not meant to be derogatory or some kind of slight of my machine or myself. That would be unfortunate as my questions and comments to you and others on this forum have been only with respect and a genuine interest in the topics at hand. Perhaps I misunderstood you? Peace....

[Cruiser]

Pete, "Your Thing" generalization only ! Brake unit, If power is off wouldn't the brake be off ! Otherwise it would have to be normally engaged and power to release. It was conceivable in my mind that there is no such thing as instantanious and that even a micro interferance with the brake might cause a spike strong enough to fault the driver out.
How fast of a spindle do you have now ? I think mine is like 5948 or close to that now.
I'm surprised about no signs of any deformation to your gibs, that is a good thing. Mine didn't get too awfully tightend but still really deformed my gib. I had to dress it up some with some smooth file action, and then re break it in for a while. It seems pretty good tho now.
It shouldn't take a lot of gib adjustment to hold the full weight of the stock gear box, and before I gutted mine it would still hold in one place and wait for use. Although, before I got the gib worn in and adjusted I did have to resort to a block of wood for when it was powered down. I had three grabby spots on my Z axis which wouldn't allow me to tighten up all at once. Once it did grab the gib and climb up over it, after braking off the cut notch portion at adjuster, luckily it had enough on other side to allow renotch and flip.
Now it appears this is turning into a war story !
Later

[BlackMoon]

while a real brake would be cool and all, what about just one of those cheap spring loaded magnetic solanoids with a 'tooth' on the end that engages into a disk with holes in it or something? id think with the right machineing config it could engage even at speed, and while it might not be the gentalist of things, its not like your head will be moving at extream speed, and this is an 'emergency' brake, not an 'every day every operation' brake.
they also have a decent amount of force if you only allow them to open a mm or two, you could use one as a friction brake too.. (though realise some are not rated for staying open at 100% duty cycle!)

[beege]

If it were me, I'd design a brake that was engaged via springs when power was off, and disengaged via electromagnets when power was turned on, and make sure it was tied into the EStop button, so that when you hit that, the brake would engage, too.

[pete from TN]

Glad I was misunderstanding the post, the written word leaves much to be desired sometimes. sorry....

Anyways, my new EXTERIOR belt drive conversion is running with a three phase 1720 rpm motor and a TECO sensorless Vector drive. I have built a two tier pulley setup atop the millhead and on the low speed I can go as slow as 140 rpm with seemingly good torque and as fast as around 1200 rpm. On the High speed pulley position I can go as slow as 1100 rpm and as fast as I have adjusted the vfd so far to show 5800 rpm on my digital tachometer. The machine is very quiet and while I have yet to machine anything with it as the cnc conversion is still undergoing the finishing stages I am hopeful it will be adequate for my needs. The high speed will certainly come in handy for the aluminum and the low speed should be very torquey with the reduction pulleys.

I am not 100% sure about it but I understand the electric brakes available actually work as the last poster described. They have a spring loaded brake of some sort and the power essentially trips a solenoid or something and that disengages the brake allowing movement. The drive should not suffer any faults. I know of two persons using them right now and have no problems with them. I was hoping I did not have to purchase one just because I am forced to be cheap but if I must I will...

You fellows are welcome to check out my threads about my conversion and the belt drive...." Finally getting started" on the benchtop forum and
"Lathemaster RF45 belt drive conversion" on the same benchtop forum...

Peace....