Interim design plan, comments welcome

[ckovacs]

I am planning on building a bigger router table now that I've cut my teeth so to speak but I am on a pretty tight budget.

I have a line on some 4x4 8020 to double as a gantry beam but with respect to the X axis (long rails for me) I was thinking of doing something like the drawing below as an alternative until I can get something better put together.

Basically I thinking of using two 2x2 sections of angle iron sandwiching the edges of my tabletop. I'd also probably angle grind the edges of the top section of AI for the V bearings.

other than being cheap and not permanent, can anyone see anything blatantly stupid about this? Seems almost too simple...




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[ger21]

two things if you go that route and want it very rigid.

1) Make sure your table is supported as close to the angle as possible, to minimize the edges of the table bending down.
2) Use at least 3/16" thick steel angle, and the larger #3 size V rollers.

[nlancaster]

I would also think shorter angle iron would be stiffer as well. Remeber those walls can flex side to side causing rigidity problems.

[ckovacs]

Thanks guys good points all around. I could either use 1x1 angle on top or weld gussets in to the inside of the 2 inch stuff. It's a temporary fix I hope so I don't know if I'll go through the trouble of welding anything.

[wizard]

It should work. You may have to do some hand work on the angle to get the two edges parallel of possibly spring load the lower rollers. You really don't want the rollers sprung so prepare yourself to figure out a way to get the edges parallel. The other potential problem is that the edges of Angle are not exactly the profile that V rollers expect, as such you might see rapid wear. There is a lot of variability in the hardness of angle iron so it is a guess as to how fast it will wear. It should hold up for the short term though.

Others have already highlighted the stiffness problem, you can deal with that by getting a very heavy cross section angle.

One problem I do see is that the angle needs to be supported for its entire run. I'm not sure exactly what im seeing in the picture but was thinking you where bolting to the rungs of the table support. You don't want any significant span and ideally you will bolt the angle on a close pitch. If the angle is unsupported anywhere you will see it twisting under load.

[cnc in africa]

Succeed and bring it over to africa

[ckovacs]

Wizard, the picture is a potential cross section of two layers of MDF and the two sections of angle iron. I was thinking of easing the edges with an edge grinding jig/sled like I've seen the mechmate and joes evolution folks use . Seems simple enough.

[wizard]

Wizard, the picture is a potential cross section of two layers of MDF and the two sections of angle iron.

Two layers of MDF isn't much. Also I'm not a big fan of MDF so you won't here much positive from me about this material. That being said the material isn't so much the problem as Is stiffness. Of course details matter but if there is any substantial span between the rails I'd want to see a thicker layup or some sort of torsion box. That doesn't significantly impact your idea here.

I was thinking of easing the edges with an edge grinding jig/sled like I've seen the mechmate and joes evolution folks use .

I suppose it would be possible but I don't think it would be easy to lash something up to correct the edges. If you vie a link to one or more of these grinding fixtures it would be greatly appreciated, I would have to imagine that this would take hours to do well.

The other problem I see here is that angle iron can be a bit soft. Vee rollers will wear at the steel so you want maximum contact. I've seen rollers wear down hardened rails meant for Vee rollers, especially where repetitive motion is had.

Seems simple enough.

It is the details that get you. As such I don't see it as a piece of cake to get substantially flatter surfaces and increase paralism between what in effect will be your upper and lower ways. I'm sure it can be done but I'm not sure I'd call it simple.

[Devastator]

Two layers of MDF isn't much. Also I'm not a big fan of MDF so you won't here much positive from me about this material. .

It makes a great spoil board, that's about it. I'm not a fan of supporting the gantry by thin wood table overhang. You will eventually see some settling/sag. Agreed on the V rollers on the steel angle, no matter how good you grind them, they will wear. Might be fine if this is just planned as a transitional machine to make parts for a better one though.

[wizard]

I see auto correct butchered my original message above pretty badly.

It makes a great spoil board, that's about it.

Even then I'm real negative with the stuff. It can be made to work but in some cases I really think it would pay off in the long run for people to use other materials for the machines base. If you must use wood a good cabinet grade wood would be a better choice. These days though you need to consider steel simply because a sheet of good plywood isn't that cheap.

I'm not a fan of supporting the gantry by thin wood table overhang.

That is what I was seeing in the pictures. Maybe I got it wrong or that wasn't the intention but the drawings sent off a few red flags. I should note though that the size of the machine here does matter.

You will eventually see some settling/sag. Agreed on the V rollers on the steel angle, no matter how good you grind them, they will wear. Might be fine if this is just planned as a transitional machine to make parts for a better one though.

I'm sure it will last for awhile. I'm just not sure awhile is long enough considering the effort required. This especially when the grinding would need to be pretty precise to maximize the contact area. The other thing to watch out for is that the cheap iron is all over the place hardness wise.

I must confess to actually thinking about building a machine in a similar way but using T-sections instead of Angle iron. One obvious benefit is that the upper and lower rails so to speak would be in the same plane and closer to parallel. Besides the fact that T-sections are harder to find I dismissed the idea simply because other approaches would be more robust and cheaper. I was also planing on a more conventional roller bearing arrangement which required wrapping at least one of the edges with three bearings. The other problem is that you need a vertical support that wraps around the T-section robustly. In the end it just seems like a lot more work than the alternatives.

Of course I haven't built a machine yet so maybe the idea isn't completely dead. However this simply doesn't look like the low cost way, nor the easy to fabricate way to a reasonably accurate and well performing machine. That shouldn't stop somebody else from pursuing the idea and was one of the reasons I wanted a link to these grinding fixtures alluded to earlier.

Just recently in another thread, a guy mentioned building a machine using flat steel for the X axis. I honestly believe this would be a better approach. I did not get the specs but it looked like the steel was at least 3/8" thick. He also had an interesting arraignment of the bearings. What I liked about this approach is that Cold Rolled steel is pretty accurate and is good enough out Of the box so to speak for a wood working machine. No grinding, fancy sleds or other special tools would be required. You still need something substantial to bolt the cold rolled to but that really isn't a big problem. The question then becomes is this still cheaper than buying supported round rails.

[dmalicky]

Keep in mind that V-rollers are inherently sloppy and flexy -- http://www.cnczone.com/forums/linear...ml#post1411350

[wizard]

Keep in mind that V-rollers are inherently sloppy and flexy -- http://www.cnczone.com/forums/linear...ml#post1411350

This has me wondering if the flat iron approach might be betterin a low cost machine. You can wrap a piece of cold rolled with bearings on the top, bottom and side of your choosing. Some flex would still be there but you would have more options to address it. Approaches like this though hardly seem cost effective considering how cheap round rails can be had these days.

[LeeWay]

If using flat bar and roller skate bearings, you do not actually need the inner bearing sets. I designed my first router with about 10 bearings per side. 6 of them were not actually needed. Each gantry side uses 4 bearings only. The bottom bearing isn't even a roller bearing, but a delrin pad to prevent lift. It runs well and is about as stiff and low cost as you can get.

My plasma cutter uses CNC Router parts carriages. They do use the third bearing. The inner bearings do not always turn. They are very close to snug, but just are not required. The third set may also help against racking, but the plasma uses dual drive on the table. No racking there.

My router has a heavy preload on those gantry side bearings. No racking to speak of on it. Lots of different designs out there that are easier to pull off than grinding Vees on angle iron and getting it all lined up correctly. Then you still don't have a lot of stiffness side to side.

[ger21]

Keep in mind that V-rollers are inherently sloppy and flexy -- http://www.cnczone.com/forums/linear...ml#post1411350

But, they've also been used for many years by Shopbot, Mechmate, and many other users.
It all comes down to what your expectations are.