I spent all day making a complex part. Lots of indexed rotations. I ended up with no usable parts. I had a series of problems. One of them was acne tension. I did a little math and my screws should not be changing tension with temperature to much. But my tensions only seem to stick for a couple of hours. Any ideas? What is the best way to set tension?
I personally think we need to grind a flat spot so the set screw actually has something to “bite” into. The screw threads aren’t anywhere near ideal…
The problem is finding the right place to grind a flat.
Well, the collar spins, correct? Just spin it unit the locking screw / grub screw seats on a flat spot (while under tension/tight). Unless, I’m thinking of it incorrectly. I know there are two screws, but as long as at least one of them has a solid hold, I believe that you would be far better off than not having either of them.
I think the R7 would be better off with a 20-30mm longer ACME. With locking collars on both ends, with a hole drilled on the non-nema end, so we could properly tension the acme. Get a good solid tension on the acme.
Corey
@Colin_Kaminski wild man, so tension. We have a post in here some where about this. A group of us drilled holes in the end of the ACME and tapped them. We moved the acme back to into the drive coupler so that the opposite end that we tapped had a bolt head that rested against the lock collar.
There are issues with this. We are working on a ball screw design right now. There is a floating end and a fixed end. The floating end does not constrain in the linear direction. A lot to read on this on the net. No system should be completely constrained at both ends. This is for temperature changes and other factors that cause the drive to change. The R7s ACME is treated in the same fashion, one end fixed, the coupler side.
You can try to reverse the end plates and put the ACME in compression like the C-Beam is originally designed. Just flip them over.
If you want to keep them in a more robust tension and add a nut, get a Tr8*8 tap and make a nut. We tried this, the constant tension caused issues with wear but the bearings on the R7 end plates are the consumables and the cheapest bearings money can buy so not too big of a deal to have to replace them often.
@Brandon_Satterfield Thank you for the update. I can get too much tension as is and compression seems hard on the long screw. If you want any help on a ball screw upgrade I would love to be an early adopter.
Another think that came to mind with your bolt idea is to put a washer on it and compress a stiff spring. This frees one end and the tension is equal to the spring tension at all temperatures.
@Colin_Kaminski I like this idea a lot.
Ball screw. This unfortunately will not be a backwards compatible mod. In fact wont be on C-Beam as it looks right now.
To your original post though… What if you just seriously fix one end and let the other float?
The ACME block (driven section) to the coupler is the only thing that matters.
What if you were to change out the flexible couplers for solid ones. I believe the motor mounting may need to be a bit stiffer in this configuration since you are pretty, well… bad ass with your machine and probably know its every limit…
Maybe widen the motor mount end plate to accept a 4 mount point set-up?
This is how we are moving with the ball screw thing.
Fixing the driven end would require a method to adjust backlash in the ACME to bearing holder. The nice thing about tension is the backlash is zero. Switching to tapered bearings and a tapped ACME would fix the bearing wear but add complexity.
Just brainstorming. When I looked in ball screws the clearance between the C-Beam and the y axis plate was the sticking point.
Are there Acme metal nuts available? @Brandon_Satterfield
@Colin_Kaminski we tried thrust bearings for a while. That was a wreck.
How bout this. Modify your end plate to accept this,
https://www.smw3d.com/nema-23-motor-mount/
Get a solid coupler.
Play with backlash with the adjustable tension nut already installed.
There really shouldn’t be any backlash with this mod. Although, now thinking about it you will probably blow the bearings in the motor.
Hmm, yeah looks like the original design may be the best here.
Ah, how bout this. Double lock collars, inside and outside the bearings. I know you push your machine and this is why the tension may be dripping off, I’ve had one running for 4 years 4-5 days a week and adjust tension very seldom. 6 to 8 months and normally only when I wreck it because I didn’t change a wore end mill or wrote bad Gcode.
So try the drill and tap of the end or double lock collars, either should remove any lost tension.
@Brandon_Satterfield Thank you for all the ideas. I am going to see what I can do as soon as I return from a conference. As a side note, I have had custom extrusions made before and the dies are surprisingly reasonable. Perhaps it’s time for the next level maker extrusion? If you need any contacts for extrusions email me.
@Colin_Kaminski I love the OB stuff. Lot of work to get production and quality running like they have… BUT I do have a couple of designs, may be worth playing with for a small group of us. Be happy to take it off-line.
Laid this out a time ago, gotta get it in CAD and mill the block. Thought I’d throw this out there, this how you stick a 1204 nut inside C-Beam.
Would these rails improve the rigidity of the C-Beam? I’ve really been able to see the flex with the z and the X beams while doing diamond drag on Granite. It’s not even at full “pressure/depth” and I get a LOT of deflection. The deflection in the X & Z limits the size of the lettering I can do because the diamond won’t move, thus wont property create the characters.
I’d be excited to see an improvement/upgrade! I’ve been looking at other options due to the flex of the R7 (mid-beam).
Corey
@Corey_Perez Odd.
Now I have never played with granite, but you got me excited about it the other day. Want to get one of these bits and have a try at it myself.
How much pressure are you having to apply downward? My assumption is the deflection you are seeing is upwards in the X?
I’m plowing through aluminum with it without issue, but this is a different animal no upward force is being applied, and honestly I never ran any deflection calcs like that when first designed.
Will it add rigidity? These rails are steel, I would would have to find the time to get the assembly in solidworks and have my guy run it through his program to see what happens. Give us some FEA based on different load conditions.
It would be considerably more rigid. I have these rails in 1000mm length, I don’t think anyone here has stuck them on either web site though. They are heavy!
@Brandon_Satterfield I can do static deflection calcs on simply supported and cantilever beams if it’s ever helpful.
@Brandon_Satterfield I just double checked, and I’m using Depth/Pressure of .25" on the Diamond Drag. It was a little less with the Mirror, but I also tried .45 on the mirror just to see if it would break/what it would look like with different depth/pressure (more splintering, less “definition”). My impression is, with the Diamond Drag bit I’m using (Diamond Drag Engraving Bit for CNC Machines - Use Your CNC Machine to Engrave Metal, Plastic, Glass, and Granite - WidgetWorks Unlimited) that the length of the tool, combined with the downward pressure is causing an amount of leverage that the R7 was not initially designed to withstand. That, in combination with being so quiet/slow, you can really see the deflection the R7 is giving. I thought about mounting my dial guage on the spindle, but aside from movement on the X, I wouldn’t have a fixed point during the Y movements. I noticed the deflection when I was trying to make small letters and the R7 was moving, but the Drag was staying stationary.
In regards to the steel beams, I don’t know if there is a “soon” timeline, but I’m retiring from the Military, and going on leave in the next 1-2 months. I’ll be headed to Normangee (TX) to pick up a few things. If you have upgraded beams, I would love to “upgrade” my R7!
Hope is, I can also pick up an industrial grade engraving laser somewhere down there for a business I’m hoping to start!
I love all the upgrades @Colin_Kaminski has done, and it has inspired me and truly motivated me to really learn and develop my knowledge of CNC and the capabilities of the R7. While no where near as smart as that guy is, I’m always finding myself trying to mimic his mods (hence the sideways Y beam addition).
Corey
Thanks bud, I can too and enjoy it. The cases are mostly dynamic though and several off axis cases to look at. Easier to let a computer do it. Have a buddy I went to engineering college with that continued to his PhD. He created an FEA software that I now buy him beer for running cases :-).
@Corey_Perez and @Colin_Kaminski you guys are the whole reason behind doing this. It is wonderful to see guys make stuff and money with the machine but love to see hacks and mods and improvements.
I really haven’t chased the HG15s and ball screws on the C-Beam, I have something else we are working on. The above image was just playing around one afternoon. We have a few other projects that have to be wrapped up before I would chance this.
@Corey_Perez If you tell me the specifics of the spring I can calculate the force. I wrote an excel sheet for it at work to make springs for pressure relief valves. I would need the free length, the inside or outside diameter, the diameter of the wire and the number of coils. A photo of the spring would be better than the number of coils so I can determine the end conditions.
@Brandon_Satterfield When I was an apprentice guitar maker 30 years ago Steve Klein taught me “every tool is a kit” and we took apart and setup every new tool. It’s amazing what you can do with a new table saw or band saw. Here is a photo from that era. Steve’s guitars are on the right and mine is on the left.
@Colin_Kaminski that’s awesome brother. I have forever wanted to make a guitar, I only have one issue, I can’t play one. My fingers just won’t work like that. Played the sax about 25 years ago, but even then stunk at it. :-). I’m a true 1 and 3 guy where the rest of the world works in 2 and 4. 