[Beachcues]

I have begun to order materials and hope to get underway shortly. It's not going to be cheap but should be very rigid. Hope to post some pictures as I get things completed. I will have questions on which screws and steppers would be best but I want to get the frame built first. If you see any areas that could be improved please speak up.
Attachment 234072Attachment 234074

[ger21]

What are you using for linear rails on the Y and Z axis?

Are you driving the gantry with a single screw?

Do you have any of these components, or are you buying everything new?

I'd ditch the V rollers in favor of profile linear guides like THK or Hiwin.

If the Z axis is using round shafts, I'd do the same for those.

If it's a single screw, I'd use two motors and screws, and get rid of all the bottom bracing tying the sides together.

Make the gantry beam out of a tube. Increase the thickness of the gantry uprights, and reinforce where they mount to the gantry beam.

Reinforce the Z axis plate to spindle connection.

Just my opinion. What might be "very rigid" to some may be "very average" to others.

[Beachcues]

What are you using for linear rails on the Y and Z axis?

Y and X are using linear rails with V rollers (why do you not like these?)

Are you driving the gantry with a single screw?

two screws and two stepper motors

Do you have any of these components, or are you buying everything new?

everything new

I'd ditch the V rollers in favor of profile linear guides like THK or Hiwin.

still don't see the advantage please explain

If the Z axis is using round shafts, I'd do the same for those.

Yes Z axis has round shafts with bearing blocks.

If it's a single screw, I'd use two motors and screws, and get rid of all the bottom bracing tying the sides together.

the bottom brace is to help stiffen the gantry beam, not a big fan of tubing.

Make the gantry beam out of a tube. Increase the thickness of the gantry uprights, and reinforce where they mount to the gantry beam.

both ends, gantry beams and uprights are all 3/4 thick 6061 not sure I need to go any thicker.

Reinforce the Z axis plate to spindle connection.

Z axis plate is also 3/4 thick with mount being 2" thick held in place by dowel pins and 4 1/2-13 shcs.

Just my opinion. What might be "very rigid" to some may be "very average" to others.[/QUOTE]

Not sure that was necessary.

Thanks for the reply I will keep your suggestions in mind moving forward.

[ger21]

Profile linear guides are probably 5-10x stiffer than V- rollers.
Same with the round shafts. They typically have some play in them, and are just not in the same ballpark as THK or Hiwin type linear guides. If you're spending a lot of money, you might as well do it right. You can get Chinese import linear guides for probably only a few hundred dollars more. Not sure how big this is, or what your budget is.

With two motors, the bottom bracing under the table doesn't really add any strength.

I'm just not a fan of mounting the spindle to the end of the plate, below the bearings, which allows the plate to flex between the spindle and bearings.

Sorry if that was too harsh. Just trying to say that different people have different expectations, and what might be great to some is very poor to others. Wasn't implying that your design is very average.

[Beachcues]

Well I can tell you I do have a budget and those rails would put me over the top, maybe for the next machine.

The machine is on the small side, my cutting area is 28" x 30" x 5" in the Z.

Would you mount the motors and screws on the sides, and attach the screws directly to the uprights?

Profile linear guides are probably 5-10x stiffer than V- rollers.
Same with the round shafts. They typically have some play in them, and are just not in the same ballpark as THK or Hiwin type linear guides. If you're spending a lot of money, you might as well do it right. You can get Chinese import linear guides for probably only a few hundred dollars more. Not sure how big this is, or what your budget is.

With two motors, the bottom bracing under the table doesn't really add any strength.

I'm just not a fan of mounting the spindle to the end of the plate, below the bearings, which allows the plate to flex between the spindle and bearings.

Sorry if that was too harsh. Just trying to say that different people have different expectations, and what might be great to some is very poor to others. Wasn't implying that your design is very average.

[ger21]

If you have room, then probably. I might also consider tucking them under the edge of the table to keep dust off of them. But I think technically, they should be higher up, applying force near the center of the load.

[ger21]

Patient Ebay shopping can get you some good deals on used THK's. There are also cheaper Chinese verisons, but I'm not sure where to find them.
At $660, these can't be all that much more then you'll be spending on your X and Y axis, are they?
HSR20LR2UU 940L THK Used LM Guide Linear Bearing 2RAIL 4Block CNC Route | eBay

[Beachcues]

I can get all the rail components for around $300 (v bearings and rails), the company I work for can get some really good discounts on materials and the little things I need to build. I bought all the aluminum,3/4 ,1/2 ,3/8 and 1/4 for under $400. The table top will be a piece of 1/2 6061 which should help to stiffen everything up. All told I should have a complete frame for around $850.00 plus a s ton of time on the cnc mill at work. Why don't you like mounting the motors to the ends and underside of the machine? Like I said I could mount them to the ends and on the uprights (in the middle of the linear rail).

Patient Ebay shopping can get you some good deals on used THK's. There are also cheaper Chinese verisons, but I'm not sure where to find them.
At $660, these can't be all that much more then you'll be spending on your X and Y axis, are they?
HSR20LR2UU 940L THK Used LM Guide Linear Bearing 2RAIL 4Block CNC Route | eBay

[ger21]

Why don't you like mounting the motors to the ends and underside of the machine?

I never said anything about motor mounting.

All told I should have a complete frame for around $850.00

You originally said it wasn't going to be cheap. $850 is very cheap. I was assuming you were spending much more than that.

[Beachcues]

Well I have some good news, I was able to get my hands on some linear rails like the ones you are talking about. They are made by ISEI which is a german company, they came off a techno cnc router. I also got a bunch of ball screws, ball screw nuts, bearings bearing blocks. pretty much everything I need for $150 bucks. only down fall with the screws is they are 16mm 5mm pitch, I asked him if they where 1 or 2 start. He said he thought they where 4 start. Does that sound right??

What one person considers expensive another may not.

I never said anything about motor mounting.



You originally said it wasn't going to be cheap. $850 is very cheap. I was assuming you were spending much more than that.

[ger21]

They're most likely 1 start screws. You probably want to gear them 1:2 to get more speed.

And I think you meant ISEL.

[Beachcues]

They're most likely 1 start screws. You probably want to gear them 1:2 to get more speed.

And I think you meant ISEL.

Probably is ISEL, it was dark when I was typing. How do I go about gearing? Belt driven or direct gear driven? The screws look like 1 start but wasn't sure, can you post a picture of the gearing? Thanks again for all your help.

[Beachcues]

I made some design changes, I didn't gear the drives mostly because I am not overly concerned about speed. Once the machine is up and running for awhile I will buy new screws and nuts. I shortened up the gantry sides and removed some of the unnecessary stiffeners. I have already purchased the steppers, drives and power supplies along with the spindle. The piece on the gantry that slides with the z axis will hold a coolant pump, radiator, fan and small tank for the spindle. I also got rid of the v groove bearings as the main linear rail system, but I am still going to use them to support the gantry sides. If you see any potential problem areas please speak up as it is still in the design stage.

Machine is all made of 3/4 thick 6061 aluminum with a few pieces of 8020 to tie the base together.

Attachment 237410 Attachment 237412

[ger21]

I also got rid of the v groove bearings as the main linear rail system, but I am still going to use them to support the gantry sides.

I really don't see the point of the V groove bearings here. For one, it would be far easier to just make the gantry sides stronger, so they don't need additional support.

The only way that they would actually do anything, is if they were preloaded against the linear bearings between them. This will reduce the life of the linear bearings, and if the alignment is not absolutely perfect, you'll either get binding in some spots, or you'll lose the preload.

[Beachcues]

I am just a little worried because I only have one linear rail ,one on each side, that some moving or deflection might be a issue. the v bearings are just for some support, as far as being perfect, I am anal when it comes to building stuff. I am used to making tools and dies within tenths so alignment wouldn't be a issue. How would you suggest stiffening the gantry sides? Like I said almost all the pieces are 3/4 aluminum.

Just for reference I showed the distance between the bearing mount and the bottom of the gantry back. once all the pieces are installed square, straight and flat I will drill and ream holes for dowel pins to ensure that it stays in place when in use. I plan to build the base then mount the linear rails, put the whole assembly on one of our surface plates to make sure the rail and tables surface are parallel. Then I will install the sides and square them to the tables surface, that is what I was going to use the v grove bearings for (they have eccentric bushings for adjustment). I see what you are saying about putting unnecessary load on the bearings, but do you think with one rail it will be strong enough to handle the side to side stresses? Thanks for your input please keep it coming, does the rest of the design look adequate?

I really don't see the point of the V groove bearings here. For one, it would be far easier to just make the gantry sides stronger, so they don't need additional support.

The only way that they would actually do anything, is if they were preloaded against the linear bearings between them. This will reduce the life of the linear bearings, and if the alignment is not absolutely perfect, you'll either get binding in some spots, or you'll lose the preload.

[LeeWay]

Those linear rails should be plenty by themselves. They are far stronger than they appear. You will be surprised I think. If you have two trucks on each rail, that is considered optimal. More is not necessarily better. Now if I was only going with a single screw, which many have done, then the V bearings may provide the preload needed to keep the gantry from racking as Ger mentioned. A single screw is not ideal though. A single rail with two trucks on each side will be very strong and pretty fast. Reducing the mass under the gantry will also make it more light weight and not necessarily any less rigid. Weight is a concern, but it isn't required on a router. Stiffness is for a better machine. If you are only using a solid plate on the gantry, it will have some give in the middle. I do see that you will brace the back side. This is good. You cannot count on the linear rails adding a lot of support in this direct. Side to side they are very strong. Top to bottom and they can flex. Consider also placing the gantry screw on the back side of the plate. That or design the Z axis so that a way cover can pass through it. Keeping the screws clean and lubed will greatly increase the machine life.

[Beachcues]

Those linear rails should be plenty by themselves. They are far stronger than they appear. You will be surprised I think. If you have two trucks on each rail, that is considered optimal. More is not necessarily better. Now if I was only going with a single screw, which many have done, then the V bearings may provide the preload needed to keep the gantry from racking as Ger mentioned. A single screw is not ideal though. A single rail with two trucks on each side will be very strong and pretty fast. Reducing the mass under the gantry will also make it more light weight and not necessarily any less rigid. Weight is a concern, but it isn't required on a router. Stiffness is for a better machine. If you are only using a solid plate on the gantry, it will have some give in the middle. I do see that you will brace the back side. This is good. You cannot count on the linear rails adding a lot of support in this direct. Side to side they are very strong. Top to bottom and they can flex. Consider also placing the gantry screw on the back side of the plate. That or design the Z axis so that a way cover can pass through it. Keeping the screws clean and lubed will greatly increase the machine life.

Yes there are two trucks on either side, I guess I will ditch the v groove bearings if I have a issue later I can always add them. do you think I will need to brace/stiffen the gantry sides?

[LeeWay]

Anytime you can add bracing without limiting travel or adding a lot of weight is a step in the right direction. You can add all the weight you want to the table and that will make it better. Weight after a certain amount on the gantry detracts from performance.
The connection point you show right now on the gantry is very weak. You are only bolting into 3/4" aluminum plate. I would actually use something like an L shaped heavy duty steel pracket on both sides. Mount it solidly to the gantry beam and the gantry uprights. You will have a whole lot more holding power that way and take up very little travel. Even a piece of angle iron would do well. Couple that with a couple bolts from the back into the gantry upright and you have something.

They (ENCO) sells small cast iron angle plates for pretty cheap especially when on sale. I keep several of those in different sizes around here for projects. Very useful and already come with holes.

[Beachcues]

Well without redesigning the gantry completely im not sure I can fit the 90deg knees. I will see if I can fit some steel angle iron inside of the rails or on the outside of gantry and post another picture. Thanks for the suggestion.

Anytime you can add bracing without limiting travel or adding a lot of weight is a step in the right direction. You can add all the weight you want to the table and that will make it better. Weight after a certain amount on the gantry detracts from performance.
The connection point you show right now on the gantry is very weak. You are only bolting into 3/4" aluminum plate. I would actually use something like an L shaped heavy duty steel pracket on both sides. Mount it solidly to the gantry beam and the gantry uprights. You will have a whole lot more holding power that way and take up very little travel. Even a piece of angle iron would do well. Couple that with a couple bolts from the back into the gantry upright and you have something.

They (ENCO) sells small cast iron angle plates for pretty cheap especially when on sale. I keep several of those in different sizes around here for projects. Very useful and already come with holes.

[wizard]

I really think you need to do something different with the gantry beam. If that means a redesign then go for it. The cast 90° angle palates might help a bit but I'd much rather see you go with a box section. It would be stiffer but you would also get more rational connections to the uprights.