Why t-slot? and free plans modifications

[quadmasta]

I searched but I guess I wasn't searching with the right keywords. Why do people use T-slot for the table itself? Is it for clamping purposes or for strength and anti-bowing/drooping?

Brian

[ViperTX]

That and cost and ease of use.

[quadmasta]

Which? In the free plans, if I were to want to make the resolution a little longer in either the x or the y axis I would just need to add the appropriate length to the table, the leadscrew, and the guide rods, correct?

[ger21]

Originally Posted by quadmasta Which? In the free plans, if I were to want to make the resolution a little longer in either the x or the y axis I would just need to add the appropriate length to the table, the leadscrew, and the guide rods, correct?

It's usually never as simple as just making everything a litlle longer. I believe the free plans machine uses unsupported shafting as guides. Adding length can increase flexing. If you're not careful, it could make the machine unuseable. There's a reason that most of the inexpensive wood machines are all a similar size. It's difficult to buils a large machine cheaply.

[quadmasta]

I understand the issue with deflection of guide rods over a certain length but can't that also be alleviated by using stronger materials for the guide rods?

[chuckknigh]

Stiffer materials, actually...OR by supporting the longer rails. But, that's just yet another modification to the original plans, and it causes a ripple effect throughout the whole project.

Anytime someone says something isn't possible...another will go out and do it. But, that doesn't mean it'll be simple.

So long as you understand what you're doing, it won't be much of a problem.

-- Chuck Knight

[quadmasta]

Someone in chat suggested supporting the rails and using a bearing that's open on the bottom to pass the support. I think that's a viable option but wasn't able to really find any info on homebrew Delrin or UHMW bearings that were fabricated in this manner. In respect to supports, the lateral movement along the longest axis of my mill (let's call it Y) would be similar, just fab some supports and maybe tap the rod to accept a bolt through the bottom of the table, through the support to hold it in place. Would a similar method work for the X and Z axis changing only the position of the bracing in regards to the nearest framed support?

Brian

[ViperTX]

It might be troublesome to have the home brew delrin bearing open on one side when the load is trying to pull the bearings off the rod (usually on the y and z axis). The x axis should be okay at the weight of the gantry will be forcing the bearings against the rod.

[quadmasta]

Originally Posted by ViperTX It might be troublesome to have the home brew delrin bearing open on one side when the load is trying to pull the bearings off the rod (usually on the y and z axis). The x axis should be okay at the weight of the gantry will be forcing the bearings against the rod.

That hadn't crossed my mind. For the Y and Z axises (axes?) I could modify how the bearings were rotated and change how the guide rods were supported as well. Let me throw something together in Photoshop real fast and see if I can explain it better.

[chuckknigh]

Wrap the bearing around more than 180 degrees and it shouldn't be a problem. Plus, if you place them in an opposing orientation ("flip" the lower guide upside down) then your motion will be completely constrained in every possible way.

Shouldn't be a difficult modification, at all.

-- Chuck Knight

[Hobbiest]

The hard part that I see is attaching the supports to the rods in such a manner. If you weld them, the rods will pull out of shape at every weld, and be noticable enough to cause problems. If you use tack welds no more than 5mm, it may not hurt that much, but penetration will be low and vibration of the machine will probably brake them loose. I experienced pretty bad warping with a pair of guide rods with less than 1" of weld at a time, and they were solidly braced straight during welding. And I was a professional welder at that time! countercunk screws into the flat stock may be an option, but could prove tricky.

[quadmasta]

Chuck: Like this?

Hobbiest, refer to 2nd picture. I was thinking about using some hex bolts to pass through the support and thread into the guide rod.