Slight delay but back on track, advice needed

[Darren_T]

Ok, I'm back on track. I have all my structural aluminum, supported Thomson rails, and just ordered my 3 Servo's. The router will have the following dimensions assuming it makes sense to everyone:

- X axis 28" with 24" rails for now.
- Y axis 48"
- Z axis 18"

It will have a moving gantry which will support a 1.75 hp router. My plans are to make the gantry sides 6" wide...too narrow? Just right? Let me know your thoughts.

The servos I chose were Jeff Davis' 360 oz/in motors with encoders. I've had a few suggestions from Jeff and others on what thread pitch I should go with for my acme rod. I'd like to get a consensus as I'm very new to this. I'd like good speed but am willing to sacrifice a little speed for torque. I want to be able to mill aluminum as I've stated before.

Any suggestions on thread pitch for my acme rod? I still need to put a power supply together and am currenlty saving for the Gecko's. I haven't looked into any other drivers than the Gecko's... are there any more cost effective ones? Just curious.

Any other suggestions would be great. Hoping to get back into building here this weekend.

Darren

[Hobbiest]

How tall will your gantry uprights be? I'd keep the gantry feet at least 1/3 the height that they will be supporting personally. Anybody got any real figures on structural stability and how it relates to hieght/base differential? Any engineers out there? I'm just a garage engineer but it sounds right to me! Always build twice as strong as you think it needs to be, and it will end up just about right most of the time.

[Darren_T]

Originally posted by Hobbiest How tall will your gantry uprights be? I'd keep the gantry feet at least 1/3 the height that they will be supporting personally. Anybody got any real figures on structural stability and how it relates to hieght/base differential? Any engineers out there? I'm just a garage engineer but it sounds right to me! Always build twice as strong as you think it needs to be, and it will end up just about right most of the time.

Well, just off the top of my head without looking at my drawings I'd say my gantry will be about 18 - 20" tall... I'll have to double check. I want to have about 6" of clearance, the router should be centered on the Z axis at a height of about 12" or so when up.

[barbwirebi]

Darren

A 5 threads per inch screw geared down 4:1 will give you 365 lbs of thrust @ 120 IPM
I would say that will cut alluminum well

Bill

[balsaman]

I would be more concerned about gantry skewing than the hight and wieght of the gantry. Make them at LEAST 10" wide, unless you are using 2 leadscrews.

Eric

[Darren_T]

I purchased 1" supported rails for my Y axis and they came with two 6" long pillow blocks. I wish I had 4 smaller ones so I could change the width to anything I like.

Any ideas? Should I buy 4 smaller blocks or is there a way to make the 6" blocks work? I suppose I could buy 2 more smaller blocks to use with the 6" blocks or will that cause problems with the design of the 6" blocks?

Thanks.

Darren

[balsaman]

If the smaller blocks aren't too expensive that's the way to go. If you do end up going with just the 6" blocks, no need to go wider on the gantry sides.

Eric

[Hobbiest]

If they are dual blocks and not just longer LB's, they shoulg have two seperate bearings in each block. I know that Thomson does this, at least sometimes. If that is the case, just whack each block in half being careful not to hit the bearings themselves and mount them however you choose.

[Darren_T]

Originally posted by Hobbiest If they are dual blocks and not just longer LB's, they shoulg have two seperate bearings in each block. I know that Thomson does this, at least sometimes. If that is the case, just whack each block in half being careful not to hit the bearings themselves and mount them however you choose.

Now there's a thought. I'll examine them and consider that. Anyone think that might not be a good idea?

[routalot]

Perhaps I misunderstand, do you intend your Z-axis to have an 18inch travel? It would seem a huge amount and would impose big loads on several parts of the structure.

[Darren_T]

Originally posted by routalot Perhaps I misunderstand, do you intend your Z-axis to have an 18inch travel? It would seem a huge amount and would impose big loads on several parts of the structure.

The Z axis rails are 18" long but the travel will only be about 8" after mounting etc...

[pack rat]

Darren T said still need to put a power supply together and am currenlty saving for the Gecko's. I haven't looked into any other drivers than the Gecko's... are there any more cost effective ones? Just curious.
There are 4 geckos 310 servo driver for sale in want ads for $225 but I would be cautious. They might be gone too.