[paul_m_hutton]

has anyone else had problems keeping the depth of their cut consistant? i was doing some routed signs using a v-bit and found by the time i had finished the lettering my depth had increased slightly. every time the router moved up and started a new toolpath it would settle a little deeper. (not much but enough that with the v-cutter it was noticeable) I run a couple of machining centres at work and I know they use what they call a 'pnuematic balancing device' to counteract the effect of gravity on the z-axis. all it is is an air cylinder that pushes up to counter the weight of the head pushing down. anyway I tried to add one to my home router and it seemed to solve the problem. the air pressure on the cylinder can be regulated so it acts like a variable spring. has anyone else tried something like this , or even had this problem?

[Rodm1954]

Hi Paul

The obvious answer is it looks like you were missing steps. The fact the router dug deeper indicates it was when Z was lifting so by adding the counterbalance you have solved the problem.

Vcarve has a lot of Z movement and it will test the Z axis in any machine.

While your fix has worked the alternative is to re-tune the motors to eliminate the missed steps.

I like the pnuematic device idea - can you post picture?

[paul_m_hutton]

thanks Rod, that does make sense. I'll try to post some pictures some pictures later today after i get home from work.

[paul_m_hutton]

here are the pics

[Rodm1954]

Hi Paul
Thanks for the pictures and a very nice looking machine you have there.

[CnoEvil]

Hi Paul,

I agree...this looks like a nice rig. Actually, it looks pretty close to what I want to do. If it isn't a bother, would you mind elaborating a bit on the specifications of your machine? I'm in the process of determining what I need (and can afford) to do when I build mine. I'm curious about what kind of force your steppers produce, cnc driver boards, power supply, etc, etc.

Love the view out of your shop window. It almost looks like I'm looking out into my own backyard. :-)

Thanks,
Mark

[paul_m_hutton]

check out this web site mark,http://www.durhamrobotics.com this is where i bought the basic machine-building one from scratch is beyond my skills as a cabinet maker. I've added the limit switches, spindle mount, cable carriers and the balancer etc. durham robotics sells the basic xyz table. I am really happy with their product. there is a picture of this machine on their site,as it looked last year.

paul

[CnoEvil]

Hi Paul,

Thanks for the reply and the link. I checked out their site. I notice in their kit that they come supplied with 140 oz/in steppers. I'm wondering, since the plans I've been looking at use something like a 200 oz/in. motor, did you have to upgrade your steppers in order to push that Porter Cable? Basically, you're using the same router that I intend to use and I'm trying to get some general idea of what kind of steppers I'm going to need to push it properly.

TIA,
Mark

[paul_m_hutton]

funny you asked mark, here is a thread i recently started http://www.cnczone.com/forums/showthread.php?t=27038 i was told by gary that the inhibiting factor could also be my computer being to slow. however i ordered more powerful steppers anyway. it does push the router around but not as fast as i would like. as soon as I receive them i'll try them out and keep you informed if it makes any difference. if you are planning to use the same spindle as me, i will post some more detailed photos of the mount i made up, as for now I'm off to work. i'll get back to you late this afternoon.

paul

[paul_m_hutton]

here are the pictures of the spindle mount.i bought two aluminum shaft collars from mcmaster-carr and had a local machine shop mill flats on them to bolt to the plate. the porter cable router is exactly 3.5" in diam.

[Rance]

Paul, I plan on doing the same thing but am having problems finding a cheap air cylinder. Do you mind letting me know where you got yours and how much it was? Thanks.

[CnoEvil]

Thanks for posting the close-ups, Paul. Looking at the specs for your steppers, I didn't realize how strong "x" number of oz/in's could be. You seem to manage a pretty heavy router with what you have. BTW, that's a nice strong looking mount.

Mark

[paul_m_hutton]

rance- this probably won't help you much but i bought it at princess auto which is a chain of stores here in canada they have a large surplus section which is where i found the cylinder, i believe it was about $20 CAD. maybe you or another member would know of a similar type outfit in the states?for what it is worth here is the site www.princessauto.com

[Rance]

Paul, Sounds like you used one of those for the back hatch of a car. That's what I had planned on doing but I planned on connecting it to a 2 litre bottle but I can't find a cylinder with an inlet port of any kind. Is that really necessary?

[paul_m_hutton]

rance the cylinder i bought is actually an air cylinder with an inlet for compressed air i have it hooked up to regulator so if i keep adding things to the machine i can increase the upforce as needed. the name "princess auto" is a little misleading they carry lots of air/hydrualic cylinders electrical components etc. i found my limits switches there too. i think you would need some way of controlling the air pressure. it took some experimentation before i was happy with the results. hopefully some of our friends from the states will jump in and suggest a place your side of the border were such things can be found for cheap.

[jcc3inc]

Gentlemen,

As to counterbalancing the weight of the Z assembly, you should consider possibly using a long extension spring. A long spring can have near constant force to extend it, and a small change in force with extension may be negligible compared to the Z assembly weight. Also, some extension springs have an initial force required to separate the coils; this is a help too. Also, they have zero friction during operation.

For the cost and simplicity, they are hard to beat.

Jack C.

[jingham]

I don't know much about steppers loosing control, but the 8020 frame work for the x and y axis could be a slight problem in depth control. I would suggest placing a dial indicator at mid-point on the bottom of the 8020 x axis and determine how much deflection is present when the gantry moves across. Same for the Y axis if there is any in the X. Nice router attachment and very clean.

[rc-cellar]

adjustable-force Gas-Spring. works great, quick-n-easy, 35 bucks

http://www.mcmaster.com/nav/enter.asp?pagenum=1101

[project5k]

i like the idea about the air cyl air spring,, i was considering a similar setup only instead of having constant supply air, i was going to use a volume chamber, plumb from the cyl to the chamber, this would increase the volume being compressed when the cyl is compressed, thus making the force over the travel more even... the larger the chamber the softer the spring rate... then i could just add air to the chamber if i needed more lift... only major drawback would be if there were a leak then it would slowly reduce the force applied... whaddya think?

[biomed_eng]

Great idea.

All you need to resupply the leaked air is a pressure regulator on your gas spring that is supplied by your air compressor.

If your air compressor breaks down and your leaks are slow, there should be enough air in your spring resevoir to still maintain the correct head forces for the required amount of time.