[Stevenpats]

Clamp the rails to the table with C-clamps and use a transfer punch to mark the holes. Remove rails and drill out the marked holes with 1/8" bit, then the proper drill size for the tap you are using, using a drill press if you have one. Using a drill press helps keep everything square. Verify everything is straight and square before you commit to marking the holes.
Steven

[balsaman]

I too noticed the leadscrew and delrin nut will heat up when high speeds are involved. It's another reason I went to the amco nuts.

Backlash is very small with the delrin. Be aware tho that it's also very hard to measure with the delrin nuts, because the delrin is springy, so backlash changes with load. You can't compensate for that in the software. It's usually not an issue, unless you are cutting very heavy material.

Eric

[ger21]

Are you still using that 1a power supply? If so, I wouold think that that's the reason you're 2 leadscrews aren't working out (the lost steps on 1). Are you setting 1 as a slave in Mach2? I wouldn't think you should be losing steps on the 1 axis with 400+ oz-in steppers. But if you're not supplying the rated current, you're not getting the full rated torque. I would guess it's either that, or you're just trying to go too fast. And more voltage would get you more speed. Before redoing you're entire setup, I would get or build a 60V, 15a power supply and see the difference it makes.

Gerry

[InventIt]

Originally posted by georgebarr
I am in the process of building my metal frame CNC. I am also using THK linear bearings. I have one question. How did you precisely drill all the holes for your linear bearings so that each hole is exactly evenly spaced? What sort of method did you use.

Thanks,

I used 3/4 cold rolled steel to attach them to. I just used a scribe to mark the center by dragging the point down the lenth of the steel while the other point hangs over the edge. The important thing in my setup was getting the two rails perfectly lined up with each other so they join correctly. Then just transfer the holes over from the THK rails and drill on center to THE SCRIBED LINE and the transfered line.

[InventIt]

Originally posted by ger21
Are you still using that 1a power supply?...
Gerry

(Please understand that I can be hard headed about some things)

To answer your Q. Yes. Only 1amp, I do think that 1AMP should be all i need to get the unloaded gantry to make rapid moves. It seems I have an alignment problem within my lead screw/motor/nut and the drag is causing the actual problem.

However... I think the two lead screw idea is a bad one. Unless they are tied together mechanically and ONE motor controls them. So most likely I will head in another direction with this. I like the pulley/timing belt setup the best.

[balsaman]

To answer your Q. Yes. Only 1amp, I do think that 1AMP should be all i need to get the unloaded gantry to make rapid moves

I doubt it. I troubleshoot for a living. If I have learned one thing it's, when in doubt, always try the easiest thing first.

Eric

[InventIt]

UPDATE...

Well, this project has taken many different changes. That’s what happens when you build without a plan I found out quickly that I have a lot to learn designing CNC tables. Anyway this is what happened.

Originally I was using one stepper motor on each side of the gantry to prevent racking. That did not work out so well since one motor can miss a step and the other motor has no idea its brother is not in the same place. I was testing rapid moves when one motor completely stopped as the other continued. It nearly twisted the whole frame and gantry out of square

The other problem I found was in the accuracy of my building of the lead screw and motor mounts/bearing mounts. All three pieces were not in alignment. This created a lot of drag on the motor as it tried to overcome the friction of the binding lead screw.

This picture shows the two lead screw assemblies after I removed them from the frame and squared/aligned the screws.

[InventIt]

After becoming very frustrated with the light duty rectangular tubing I was using, I decided to scrap the first frame and make a new stronger frame. The new frame is made from 2” square steel tube 1/4” wall. This tubing is much straighter and the sides are flat and square. Also the small linear bearings I was using were looking like they would be too small to hold up to the forces of the router and the weight of the gantry. So I got some wide THK RSR15 linear bearings to replace the smaller ones. These larger bearings fit perfectly on the 2” tubing.

This is the pic of the second frame.

[InventIt]

Here u can see a mockup of the new wider THK bearing sitting on top of the 2" sq tubing frame. Fits perfectly.

[InventIt]

In the last pic the bearing was mounted directly on top of the tubing. I thought it would be better to make the design more modular. So I mounted the bearings on a piece of flat cold roll steel and then I'll bolt the steel assembly to the tubing frame. This gives me adjustment of the linear rails.

[InventIt]

Bearing mount for the leadscrew. (That's not where it goes, it's just sitting there for the pic.) U can see the other on mounted under the rail.

[InventIt]

This is the other end of the lead screw mount. The timing belt pulley will mount between the blocks. Both blocks are loaded with a plain ball bearing to support the lead screw on both sides of the pulley. This will eliminate flexing of the lead screw when the belt acts on the pulley.

[InventIt]

WELL...

This is where things go in another direction again I found this beast at the metal supplier. 6” tall 4” wide and ¼” thick. This is going to be my gantry. I’ll attach my THK linear bearings to the 6” side of the tubing to make my X and Z axis.

Can u say ridged....

[InventIt]

Here the gantry is just sitting on the linear bearings to get an idea of what I’ve got.

[High Seas]

MASSIVE! WOW-OOO-WOW. THAT IS BIG! Don't let the gantry slip off the ways! You'll dent the floor.
:cheers: Jim

[InventIt]

As u can see, I have seriously strayed from my original design. I wanted to make a plasma cutting table that could double as a router table. There just are not enough similarities in the two types of uses. The plasma needs fast movement, only two axes, and can be made from a light frame. The router table needs a sturdier frame, three axes, more clearance under the gantry, and slower speed. So, this table will most likely have to be dedicated to CNC routing and hopefully some light duty alum milling. I guess I'll just have to make a plasma cutting table too

Here is that beast of a gantry wearing its new linear bearings. I salvaged the smaller bearings and mounted them parallel to the larger ones to help prevent flexing of the Z axis. BTW, I have 40” of movement on the X and 38.5” on the Y axis. Plan on at least 10" on the Z axis.

[ballendo]

Hello,

I won't argue that you're hard headed...

Why do you "think" that only 1 amp is enough?

I'm willing to bet it's not! And others have said so too...

What is the motor rating?

(Hint: If the motor rating is more than .25 amps, you're not being hard headed, you're ignoring reality...)

While a stepper won't use the full current ONCE it is at top speed, it DOES require current to get there...

The RESULT of your self-imposed limitation is good, IMO. Using one motor is nearly always a better idea. Having said that, there are a LOT of commercial machines --and homebuilts-- that work well with two motors. But they don't try to starve the motors for current becaust they "think" it's okay

Why not use a chain or timing belt across the machine to drive the 2nd screw. There is no need for the motor to be in the middle, so just change one motor mount plate to a bearing and make screw extensions to mount the pulleys...

Hope this helps, I sure don't understand why you won't try more amps... Oh well, to each his own.

Ballendo

Originally posted by InventIt
(Please understand that I can be hard headed about some things)

To answer your Q. Yes. Only 1amp, I do think that 1AMP should be all i need to get the unloaded gantry to make rapid moves. It seems I have an alignment problem within my lead screw/motor/nut and the drag is causing the actual problem.

However... I think the two lead screw idea is a bad one. Unless they are tied together mechanically and ONE motor controls them. So most likely I will head in another direction with this. I like the pulley/timing belt setup the best.

[InventIt]

Here is a good way to convert your drill press to a thread tapping machine. Just took the motor belt off the pulley and use my cordless drill with the clutch set to prevent the tap from breaking. Takes a little coordination to hold the drill and guide the spindle into the hole, but it taps straight.

[InventIt]

BTW, I am using spiral flute taps. These taps are awsome. One pass right through and the swarf comes OUT of the hole as a single twisted curl. Just like a drill bit.

[ballendo]

Hello,

Since you appear willing to start over to improve things, you may want to put those expensive bearings on the SIDES of the frame, where they won't be as likely to attract dust and swarf. Don't forget to plug the mounting holes; it's easy for stuff to get in there and then from there into the bearing tracks themselves.

Moving the linear bearings will also make the machine stiffer. Take a look at the load directions and values for the bearings you're using...

Hope this helps,

Ballendo

P.S. Modern linear bearings often fail the TLAR test. Because we just don't believe that the small bearings can give the load ratings claimed. But they DO! The bearings you have now are FAR, FAR in excess of what's required...

TLAR= That Looks About Right

Case in point: Thomson improved their line of ball bushings so that you can basically use the next smaller size. But they report that the "old" sizes still sell as before. because when people go to purchase the item built using the "new" bearings, they fail the TLAR test, and the sale is lost. MFRS. realise this and use the bigger sizes even though the engineering doesn't need it! Ah, Human nature

Originally posted by InventIt
Here the gantry is just sitting on the linear bearings to get an idea of what I’ve got.