required table speeds

[diycnc]

what type of table speeds would i need for a 50"x50" table?

i want it to be a multi purpose machine. it needs the ability to mount a plasma, router or torch to it.

i can get 5mm pitch screws witch would max out at 140ipm, would 140 ipm be sufficient until i can upgrade to 10mm pitch screws (280ipm)?

i plan on using kelling NEMA 34 MOTOR 640 oz-in. with they even do 700rpm?

rpm 700
steps per rev 200
multi step 1/2
screw pitch 0.2
travel per step 0.0005
pps 4666.67

[TOTALLYRC]

For thin material, I hear that it could be as fast as 400ipm to cut properly, so you need to decide what you will be cutting and how fast the plasma needs to go.
On a table that big, for routing wood, I would consider 200ipm the minimum speed as I can't stand waiting 30-40 secs for the machine to travel from one end to the other.
200ipm is still going to take 15 secs for full travel.

700rpm on a 50" screw will probably whip and shake, but I use rack and pinion so I am not 100%sure.

You should be able to search for router builds on the zone and see what people use for similar sized machines.

I think that 700rpm from a motor that size is asking a lot but look at the torque curve and see what kind of torque the motor has a 700rpm.

[BobF]

1/2-10 5 start screws give an effective pitch of 2tpi. you could run 200 ipm at 400 rpm.
Do you really need nema 34 motors and 640 oz in?
Most of the router tables I have looked at run on 200-400 oz in nema 23 motors with no problem, and usually higher power motors actually give lower speeds.

[diycnc]

i really dont know what i need. i do need it to be able to router out aluminum. so i figured the motors in the 640 range would be good. also looking at what the mechmate guys use.

also if i end up going to 10mm pitch or 15mm pitch i dont want to have to buy new motors to be able to turn them.

[BobF]

Look at some of the sites of commercial screw suppliers, they have info on calculating the force from a screw based on motor torque and screw characteristics. I calculated the force generated by my 305 oz in motors based on my 1/2-8 2 start screws and some assumptions (I used screws from one source and info I found at another). I get around 200 lbs. I know the machine had no problem cutting an aluminum edge I put in a channel in the mdf bed for line up purposes during an oops.
I don't normally cut aluminum, but I cut thick hardwoods with a 1/2" diameter bit, and I have never seen any evidence that the machine needed more power.
If you cut aluminum with a router, you usually take multiple small cuts.

[johnmac]

diycnc, BobF is right. Keep in mind that stepper motors produce best power at slow speeds. If you use acme screws, you want at least 2 starts. For the length of the screws you need, consider larger than 1/2". A long screw will want to sag. That's what will make it whip.

John

[diycnc]

if i use 282 oz motors to cut at 80ipm with a 5mm screw i end up with 279lbs force but my table is maxed out at 140ipm (700rpm) at 140ipm i have 195lbs

now if i find i am not happy with 140ipm and decide that i want to shoot for 400ipm i would need a 16mm pitch screw, i end up with 198lbs at 80ipm at 400ipm i have 61lbs

with a 640oz motor on 16mm pitch at 80ipm i get 367lbs