New Machine Build Yes. Another RF-45 clone build (Grizzly G0762)

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Thread: Yes. Another RF-45 clone build (Grizzly G0762)

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    Default Yes. Another RF-45 clone build (Grizzly G0762)

    This post is just a placeholder for now, but I finally bit the bullet and bought a rf-45 clone machine that I have been wanting for a while. I have a G0704 that works fine,but have wanted the Grizzly G0762 ever since I saw one while visiting the Grizzly showroom while on vacation about 3 years ago. This machine already has a vfd and 3 phase motor and I believe with re-programming of the vfd could be made to go a bit faster. We'll have to see on that though. The trigger for finally buying it was when I saw that the machine is aon closeout at Grizzly for $2195 from its list price of $3493. The machine is essentially the same as the G0761, but with the vfd and 3 ph motor. I won't need the power feed it comes with but the price of the G0762 is actually less than the G0761 right now and only a little more than I could find any other rf-45 clone for..

    Anyway, the plan for this machine is 20mm ballscrews with double nuts on each axis. The drive type for the axes is still a little up in the air, but will be closed loop of some type. I haven't ruled out closed loop steppers but am leaning toward either DC servos with gecko drives, or DMM AC servos. I'll have to weigh the pros and cons before I make up my mind. I'm hoping I can eek out 9" y-axis travel From one youtube video I've seen it appears that is possible as the limiting factor on the travel as it comes from Grizzly is the big switch box for the power feed. It sounds like just removing that gets you 9" travel with a modest amount of overhang of the base. I'll know in about a week once it gets here.

    The first things I'll be doing are building a temporary wood stand to get it to a comfortable working height, then disassembly of everything for measurement for the conversion, and also to verify that the head internally is clean. I've read too many horror stories about rf-45 clones that had grit in the gearbox. Then it will take some time for me to design my conversion. I figure each brand of the rf-45 clones probably has enough variation that other designs would at least need verification.

    I'm going to try to hold onto my G0704 long enough to make the conversion pieces for the G0762, but in order to avoid sleeping in my workshop I promised Mamma that I would be selling the G0704. I'll have to see how long I can hold her off.

    Here is a stock picture of the machine I bought.

    Yes.  Another RF-45 clone build (Grizzly G0762)-g0762-jpg

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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    I got word that my new mill will arrive on Monday. In preparation I am going to build a temporary stand out of wood to get it to a comfortable working height. Even though this is a "temporary" stand, the machine will likely reside on it for at least a little while after the basic CNC conversion is complete. For this reason I want it to be at a good working height. I'm thinking about a height of 24" from the floor to the top of the stand which would put the table about 34" off the floor and seems like a pretty good height.

    What floor to bottom of mill base height are you guys that already have your RF-45 type machine using, and is that height working out OK?



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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    Not much action but I'm going to keep posting anyway.

    Well the mill came Monday just as expected, but I have been sick and all I could muster was to drive my skid loader enough to get it from the delivery truck and into my shop. I haven't even opened the box yet.

    I have been continuing to mull over the axis drive options. The DC servos were formerly the top of the line option for home shop CNC machines, but with the advent of lower cost AC servos and closed loop steppers that has become a bit clouded. I have pretty much eliminated the DMM AC servo option due to price and being locked in to one vendor. This leaves the closed loop steppers and the DC Servos, both of which are available from many sources. Price is comparable for the DC servos and the closed loop steppers so it really boils down to performance, ease of setup and reliability.

    My desired performance isn't all that high. I want about 200 IPM rapids and 100 IPM for cutting but not hogging type cuts. Should be pretty attainable with either system.

    As far as reliability, I doubt that I would ever wear out any system I chose since I am just a hobby user, so reliability would come down to non-wear component failure. I don't see tons of failures on the DC servo setup online although there are some, but it appears that most common is a drive failure but Gecko has a great reputation for supporting users, which is a big plus.

    The closed loop steppers on the other hand have very little online information about reliability. Maybe this is because they are very reliable. One thing I think about is the fact that if I go the closed loop stepper route I would have to buy drivers that are basically copies of Leadshine drives due to price. Using genuine leadshine would eliminate them from consideration. Using copies means I hold no hope for product support which is a consideration.

    I'll probably go with belt drives for either system to keep the overall machine footprint a bit smaller, so that isn't really an issue as far as complexity. Ratio would be 1:1 for the steppers and 2:1 for the servos. We'll see how that pans out.

    There aren't many rf-45 type builds with closed loop steppers. Actually the only closed loop stepper build for an RF-45 I have found is KCJ's, which is quite impressive and appears that it would do what I want it to do. I also found a link that shows a PM-25 (G0704) using 283 oz-in closed loop steppers and he is able to get much higher rapid traverse speeds than I can get with the 570 oz-in motors I have on my G0704. This seems to confirm that the closed loop steppers are much more capable than their open loop counterparts. Here is that video.

    https://www.youtube.com/watch?time_c...&v=KuX1QdGcGJ0

    In a nutshell, I have ultimately decided to go the closed loop stepper route because it appears that it will do all I want and is a bit easier to setup. I just now have to decide if I want to use drives that need a separate power supply or use the ones that are available to run off line voltage.



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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    I would do the closed loop over the brushed servos. I have run the brushed for years and they work OK but they really dont have much of a power advance over steppers, You be surprised how easy it is to reach the 20A peak on a Gecko drive and then they fault. It not better than a closed loop which keep trying trying to catch up.

    The one advantage of the Clear Path Nema 34 servos is they are perfect for direct drive and the short ones have way more power than you need for the X and Y. You might want to add in the cost and time of the belts and then compare to the CP servo and direct drive. I have one and its a nice short powerful servo.

    Without a belt drive I'm not sure what you can cut at 100 IPM.

    youtube videos of the G0704 under the name arizonavideo99


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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    Quote Originally Posted by arizonavideo View Post
    I would do the closed loop over the brushed servos. I have run the brushed for years and they work OK but they really dont have much of a power advance over steppers, You be surprised how easy it is to reach the 20A peak on a Gecko drive and then they fault. It not better than a closed loop which keep trying trying to catch up.

    The one advantage of the Clear Path Nema 34 servos is they are perfect for direct drive and the short ones have way more power than you need for the X and Y. You might want to add in the cost and time of the belts and then compare to the CP servo and direct drive. I have one and its a nice short powerful servo.

    Without a belt drive I'm not sure what you can cut at 100 IPM.
    Thanks arizonavideo. As for cutting at 100 IPM, it would only be either wood carving, or 3d profiling at those speeds and I would likely start with some kind of auxiliary spindle. I will likely end up making a belt drive for the spindle down the road sometime.

    I did finally decide on the closed loop steppers. I'm going to start with the XY and use a 8 Nm steppers running from 110 VAC input drivers. I'm still thinking I will belt drive the table ballscrews to keep the footprint as small as possible, but I'll make the final decision on whether to belt drive them once I get the motors and see where I can best fit them.

    BTW, I finally got the machine unboxed and up on the temporary wood stand, but not anything more than that. Next will be temporary wiring to test the spindle, and then XY table disassembly will begin as I can find time to do so.

    Yes.  Another RF-45 clone build (Grizzly G0762)-g0762-1-jpg



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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    For a X axes belt drive to save space others have located the stepper at the back side of the table flipped inward.

    It should clear the column and it wont stick out the front.

    youtube videos of the G0704 under the name arizonavideo99


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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    Finally got a chance to work on the machine the last couple days. I got the table and carriage disassembled, measured and designed my X and Y axis components. I have decided to go with a direct drive on the X and a belt drive on the Y. The reason for the direct drive on the X is because I realized that if I use a belt drive I would have to sacrifice a few inches of X-axis travel, and I don't want to do that. I'll just deal with the motor sticking out.

    The plan is to get the Y axis under motion first. I bought one motor and drive that I want to test out. If it works out I will just go with the same on all 3 axes. It is the 1700 oz-in closed loop stepper that Automation Tech sells. I'm a bit worried about the motor inductance, which is kind of high, but the drive is an AC drive that hooks directly to 110 VAC. If the drive just rectifies the 110 VAC, that would be 155 VDC, which could offset the high inductance. We'll see. The drive is essentially a copy of the Leadshine AC drive, but limited to 6A output, which is what the motor is rated for. I'm hoping that it works out.

    Today I got the Y-axis ball nut mount and the bearing block for the angular contact bearings for the Y-axis screw fabricated today. I forgot to get any pictures though. I'm not mounting the angular contact bearings in a housing with rubber seals. I am making pseudo labyrinth seals, so I just need to make those for the Y axis and then I can get is mounted to the machine. I'll have to wait for my pulleys and belts to arrive before I can get it under power though.

    More to come.



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    Default Re: Yes. Another RF-45 clone build (Grizzly G0762)

    I've got the y axis done except for a proper motor mount and belt guard. I also have the call axis getting very close. My pulleys and bells came so I put them on the y axis, clamped the motor to the stand to test and got the y axis under power. I'm testing right now Ruth grbl, which only guarantees 30 kHz step rate. With 1:1 belt drive, 5mm pitch screws, and 1600 steps per rev that calculates to about 220 Ipm . I can move all day long at that rate without any problems. If I bump up to 250 Ipm, the drive faults, but that is at almost 34kHz on grbl. I don't know if this is because the step signals from grbl are getting messed up or if I have just found the limit for the motor. More testing will get to the bottom of it.

    I also have the x axis mostly done except for locating and drilling the mounting holes for the motor mounts. Got slowed down waiting for a new belt for my tool post grinder because I had to shorten the x screw and turn the cut end for the floating end bearing.

    Still no pictures but will get some soon. I'm kind of too embarrassed about the mess in my shop to release any pictures of it in that condition.

    Last edited by 109jb; 12-24-2018 at 01:32 PM.


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Yes.  Another RF-45 clone build (Grizzly G0762)

Yes.  Another RF-45 clone build (Grizzly G0762)