[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.

[balsaman]

Gecko's are the cheapest servo drivers, and the best.

Eric

[Hobbiest]

Darren T,
8" is still a lot of travel for a non- quillfeed machine. The average router is no more than 7" tall, with a MAX of two inches bit length (and that is stretching it!) That puts only 1" of the router above the lower extemeties of travel. In other words, if you have a stick jutting out the bottom of your car and drive over a speed bump, it will bend at least! At least consider using trusses of some sort on the mounting bracket, even make little I-beams. I am paranoid most of the time, but if you want to do a lot of metals, make that darn thing as strong as you can! You could use channel for your mounting bracket, but as channel is the weakest when oriented to bend against the perpendicular face, add a couple of pieces bar stock to the edges. In effect you will have an I-beam on both sides of the router, with channel going the other direction. In other words, use the best engineering qualities of each, and make it redundant! My two cents...for what its worth (sometimes more than two cents!).
Did you check out if there are two bearings in each block? Cheers, Jens

[Darren_T]

Originally posted by Hobbiest
Darren T,
8" is still a lot of travel for a non- quillfeed machine. The average router is no more than 7" tall, with a MAX of two inches bit length (and that is stretching it!) That puts only 1" of the router above the lower extemeties of travel. In other words, if you have a stick jutting out the bottom of your car and drive over a speed bump, it will bend at least! At least consider using trusses of some sort on the mounting bracket, even make little I-beams. I am paranoid most of the time, but if you want to do a lot of metals, make that darn thing as strong as you can! You could use channel for your mounting bracket, but as channel is the weakest when oriented to bend against the perpendicular face, add a couple of pieces bar stock to the edges. In effect you will have an I-beam on both sides of the router, with channel going the other direction. In other words, use the best engineering qualities of each, and make it redundant! My two cents...for what its worth (sometimes more than two cents!).
Did you check out if there are two bearings in each block? Cheers, Jens

Check this out... it's my Z axis. It's two supported 3/4" rails mounted with carriage...it's gonna be quite sturdy...the whole machine is going to be overbuilt. Excellent advice though and I thank you. I need all I can get as this is my first machine and I'm quite new to this. I'm mechanically inclined but quite green with CNC machines.





Right now my weak axis is my X axis...it's unsupported 3/4" Thomson rails. I wish I had supported rails for this axis but couldn't find the right deal...I'll change them out someday or sooner than that if it causes problems. My Y axis is supported 1".

[Hobbiest]

Why not swap the Y axis for the X axis? This also has the added advantage of putting the shorter of the two in the least dimensionally stable position. The wider you machine, the more the gantry will want to yaw. With the x axis, I was refering to the actual bracket for the tool. The axis itself looks very stiff, but the bracket will still overhang. Mock up a bracket, and see it at fully extended as well as contracted, and you can see what I mean. What did you ever find out about the pillow blocks?

[Darren_T]

The pillow blocks are due to arrive today so I'll be able to tell if I can cut them in half effectively. I think that is a great suggestion if it will work.

I need at least 24" for my x axis so I can cut large foam letters etc... The 18" would be far too small since my effective width would only amount to around 14" max. With the 28" wide gantry I should be able to get 22" widths which should suffice. I have tons of aluminum so a stiff gantry shouldn't be too much of a problem. At least I hope

I'll swap my unsupported x axis rails for supported some day hopefully.

I'll be building my bracket support for the X axis out of 1" aluminum so it should prove to be quite rigid. One way or another I'll be sure to get it right. I'm sure you guys will have much good input on that.

Do you think I should limit my Z travel to about 4"? I know I want to cut 2" material when cutting foam letters etc... I think I could limit it to 4" without problems.

Racking...hmmm... should I consider dual lead screws with a timing belt driven by one servo?

[Darren_T]

Just got my supported rails with 6" pillow blocks. Each block is built with two sets of bearings and could be cut down the middle but there is no rubber seal on the inside of the bearings, just the outside. It looks like I could buy some new rubber seals and put them on if I'm thinking correctly. It seems a shame to cut them apart though because they are so nice.

[Hobbiest]

But you need the spacing! I think that limiting the travel would be a good idea. The only reason really that it would be nice to have the extra travel, is if you wanted to put something taller under the cutter. But you wouldn't be able to carve 3D pieces very deep with a router or Dremel. Bout 2" would be max I'd say. But hey...some of the foam is 4" thick. Don't forget to account for the length of the cutter when designing you axis, as it does no good to have the collett go all the way to the surface plate.

[Darren_T]

Originally posted by Hobbiest
But you need the spacing! I think that limiting the travel would be a good idea. The only reason really that it would be nice to have the extra travel, is if you wanted to put something taller under the cutter. But you wouldn't be able to carve 3D pieces very deep with a router or Dremel. Bout 2" would be max I'd say. But hey...some of the foam is 4" thick. Don't forget to account for the length of the cutter when designing you axis, as it does no good to have the collett go all the way to the surface plate.

Yeah, I think I'm going to try and still get more than 4" clearance because I'll be using a 1.75 hp variable speed porter cable router. I do plan on doing some 3-d stuff eventually also. I guess I'll have to build it stout!