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- เผยแพร่เมื่อ 12 ก.ย. 2024
- The knee is moving but now we have another problem - ballscrew backdrive!
Can this gas strut help?
If you want to see how I got to this point in the build check out this link to the playlist:
• Ep 1: Drill Press Upgr...
And for the CNC machine build (short version) check out this playlist:
• DIY CNC machine direct...
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Good day
I have designed a small scissor lift to lift and lower my drill press table. I just have an 8mm acme screw to operate the lift. I have now used it for at least 2 years without any issue and am very happy with it as it is the best mode I made
Regards
Sounds like a neat solution!
I would not balance the weight completely, because any backlash in ballscrew will be worse,
I would have some pressure down, so perhaps go down to 250 ? That will help allot on the backdrive, and most lilkely stop it from dropping, and there will be some preload on that ballscrew at all time to reduce backlash
Most likely also solve your problem on the rotating ballnut lifting up as it will have some pressure down still.
I think you are right. I’ve got another strut on order so let’s see if that helps.
My background is in robotics and I spent a while designing robotic actuators. I think the brake you showed is a good solution. If 2n.m proves too little, you can also get the same style brake but with interlocking gear teeth instead of friction discs. These can obviously withstand ridiculously high torque, and with these you'll never have an issue with backdriving even with a heavy load on the table. They tend to be more rare an expensive however.
Ok thanks that is good to know!
Ideal solution is to drive the Ballscrew with a worm drive gearbox. If the speed is too low, Use a speed increasing belt drive to drive the worm.
I did look into that but a worm gear set was quite expensive and then I needed to gear it up. I’ll keep working on the ballscrew as I think it is nearly there.
After you're done and have finally found a working solution I'd love a cost breakdown. You know with the bigger stepper, the aluminium stock, the new drive mechanism, the two gas struts, etc. vs just buying a servo with a brake.
Ok I’ll try to compare. At the moment this is cheaper but probably not easier!
That back drive shows how efficient the ball screw is; which is a good thing.
Ok yes there is that.
@routercnc9517 I've noticed that during the final testing faze you didn't bolt the vise on to the table. The added weight from the vise and the billet that you put in the vise ( although that I don't think is going to do much , judging by the size of the drill press you're not going to mill some heavy stock) they might help the motor overcome the gas strut.
Yes you are right that would have helped. I still want the balance point to be much lower and probably need to go much lower pressure. I’ll have a play when the next strut arrives. Thanks
ues an ecteronic Brack like the one on a mobility scoter that coms on when the motor is trend of the brake brings a mobility scoter to a dead stop . it wold com on when you servo id at rest 7 com of when your motor as power the electro Magnet is energised when the power to the motor is at rest the braking the unit thus stopping creep & off when the motor is engaged & the break coms off, some have the siting on the top of the scooter motor parps you should ues one of there motors & mount it sideways on a gear.
I need a brake which is ON when there is NO power (drill is completely switched off) otherwise the knee will lower when I am not there! Is that what you are describing, or do they need power to apply the brake? The cable operated disc brakes I fitted to my daughter's e-kart project were spring loaded to the OFF position, with pads pushed away from the disc. Pulling the cable against this spring activated the brakes, so the whole concept would need to be reversed so the pads are held against the disc with a spring, and power/motor/solenoid is required to pull the pads off the disc when you want to move the motor. This is how the stepper brake works.
Can you perhaps explain what you mean a bit further? Thanks
Where's the break-even point at which it would be better to get rid of the knee entirely, and get Z movement from raising/lowering the drilling head? Is it just comparing the weight of the loaded table vs. head weight?
I've got projects enough for two lifetimes already, but if I was going to build my ideal drill it would be a 'bed' style.
I think at that point I would just start again. And if I did that I would make it into a milling machine!
Its an unknown fact and maybe just an opinion, but for Z axis you gots to go rack ‘n’ pinion!
The very original hand crank on the table was rack and pinion driving through a worm gear. But it would take too much work to get it to fit on the new machine.
Why not purchase an adjustable gas strut so you can set it exactly where you want it. I used these on my mill and without the leadscrew connected I set the unit so I could lift the head without much effort but it was still able to support its own weight. The only problem with these units is they can only be adjusted once so you need to release the gas very slowly.
I did look into those - they had a grub screw to bleed the pressure. In the end the fixed units are only £13, so not too bad to experiment with.
Ого 😊. Какой станок у вас находится 😊
Мощный.
Я ..под ..ся,. Вы?
Hi, why don't you put a counterweight at the back of the machine (parallel to the z-axis)? In this way, there is no excessive load on the top and bottom.
I did look into that but there was not much space for the size of counterweight needed. Thanks
500nm is to much I work with gas struts there should b a nipple on the fat part of the strut the top and screw there should be a bleed valve in there. If you press it, you’ll be at take some pressure out.
Yes I saw those adjustable types but this is a cheaper fixed unit. A lower force one arrived yesterday and is much better.
@@routercnc9517 sometime they come in to much I have to depressurising them but glad u sorted it
OK thanks
I'd go with the hydraulic disc brake.
It is an option still but a lot more work. I’ll have a look at the stepper brake when it arrives and see which way to go.
Can you not add another nut to the lead screw that is controlled by a linear actuator and a leaver that jams it up when the power is off?
Not sure that would lock up the screw as the ballnuts are very efficient even under load. Have you seen it done or tried it?
@@routercnc9517 I’ve not worked with ball nuts before. Just new to the channel and thinking aloud. Can a nut be bought without the balls that’ll fit the ball screw? If it can be done then it’ll be a simple cheapish way of doing it without introducing additional moment
The nut would just move freely over the ballscrew without the balls. They don’t make them to fit the ballscrew directly.
You don't want a neutrally buoyant load. You want the motor to always be lifting. Size your gas strut appropriately.
For someone who's clearly been to university for engineering, I keep finding myself wondering if they taught anything.
Balance point in the middle of travel minimises the maximum load on the motor meaning faster travel and more chance I could drill with a canned cycle. I’m not worried about backlash when the load changes from positive to negative since the backlash on the ballscrew is 50 microns. With a leadscrew then yes I would have a very low gas strut force and always have a downward net force. Thanks
@@routercnc9517 I worked on multi million dollar CNC machines... You're right...I don't know what I'm talking about
I'm having the problem of my Z-Axis on my small homemade CNC dropping when power is turned off. I looked at brakes but I wasn't sure where I'd generate the voltage to control the brake. I'm in the process now to install a 10:1 planetary gear that's designed for NEMA 23 motors like I'm using. I'm hoping it works. Right now the back driving is actually enough to light the LCD meters that monitor the 70 VDC power supply for the motor. The motors are actually servos made by Teknics. Has any one else tried anything like this?
My brake will be powered off a 24V power supply and will be relay controlled by the Arduino.
Many years ago I was told not to allow the motor to feed power back to the driver (by the driver company).
I'm late to the party but YT won't stop recommending this channel. Can someone tell me WHY this project has been undertaken? Is it an educational venture? Content for the sake of content?
If you check out episode 1 it will show you the frustrations and limitations of the original machine. This series tries to overcome all those and make it more fun to use. I enjoy tinkering and designing and sharing my experiences.
Check out the playlists on my channel, and if they are not for you I think you can tell TH-cam to stop recommending my channel to you by right clicking on the thumbnail and clicking ‘not interested’. Something like that anyway. Edit - OK, to the right of the thumbnail are three dots. Left mouse click for options, including "don't recommend this channel". Or if this content suits then feel free to follow along!