Now Cutting! - Auckland NZ

[KenC]

I personally prefer cutting from 1 side & weld-shut the height once it is decided.
PS, the height will not be dead on... BUT do your best to keep them within 1~2mm variation (remember, think slicing/rubbing). The shims will do the rest in the later part of the build.

[litemover]

Ok, just finished cutting down my rails, they are hardly precision cuts, kind of jagged. I'm hoping the grinding will make them a bit more precise. The second X rail, I cut 1mm higher so I can have some leeway to grind it down a bit more precise.

[smreish]

Chris,
Did you put a grinder disk in after cutting down and make a few passes to even out the top profile.....like a surface grind making it really flat before you start profiling?

[litemover]

Hey Sean, thanks for the tip. Going to do that today. Unfortunately, one rail was cut from 28mm to 25mm slanting one side to the other due to the cutting disc not being perfectly level. May need to do that one over...

[litemover]

Just a quick question, if I want to weld 2 offcut angle irons together to make up a new Y rail, would that be advisable? I need to cut down a new rails one of my rails were cut to 25.51 mill.

Many thanks,
Chris

[Alan_c]

What process/system are you using to cut your rails down?, using the sled I made enabled me to achive a total variation along the full x length of 0.2mm!
see here:http://www.mechmate.com/forums/showt...3&postcount=45 and lower down in post 57.

[litemover]

That's sweet. Wish I had seen that one prior to doing mine. I used the skate. It's ok, and the last one turned out pretty good, but the other ones aren't that great. I'm going to need to grind them down with something to get them flat. Perhaps I ought to use something like this but with a grinder head, instead of the skate.

[Surfcnc]

Hi Chris

Steady as she goes on the rails - 3mm variation is not good enough so ditch it and consider that as practice.

Treat the rail cut as two parts ..
1. remove the bulk
2. fine tune the height

As Alan has suggested the plate mounted grinder works great.
Set up on a straight surface, I used my X beams and then grind down the top of the rail square and to an exact height using successive passes.

When I say grind I mean sand.
Use a fresh grinding disk with a sanding disk as the cutting surface.
Start at about 40 grit or rougher then go up to 120 for a mirror finish to the rails.

My thread details the methods used. Sanding the rails will vastly improve the surface finish and significantly shorten the time you spend making the rails.

Regards
Ross

[litemover]

thanks, by ditch do you mean completely start over and buy new angle iron? Just curious, what is the lowest I cut the angle iron down to? Can I re-cut or sand them to 25mm or 24mm? if so, then I would be able to get them nice and even. I've been cutting on my X rails, but I don't think they are too flat either. I definitely underestimated the level of precision needed for these. The two long rails are 28mm for most of the rail, then they dip down to 25.5 and 27mm toward one end.

Been working low coz my xrails are quite heavy, hard on my back.


photo sharing

[Surfcnc]

Hi Chris

It is up to you to determine if 25mm is enough.
When the plans say specify something that's what I do.
"Ditch It' means recut one at the correct height.

If you have 3mm variation in height I suggest you have a real problem with your method.

1. Don't work low - get some tressles or saw horses and a few blocks of thick timber and lift one beam up on them at a good working height.
2. Look at this post http://www.mechmate.com/forums/showt...&postcount=186 and copy my setup.
3. Note you clamp the rail to the board and the beam and cut the rail from the back. It is impossible to get 3mm variation using this method.
even if the beam was bent over its length the rail is bent to match that and the cut remains at a consistent height.

Ross

[litemover]

Hi, thanks for the info here. BTW, the inconsistency didn't come from the cutting, they cut initially within .4mm, but since one rail was off to the other, I thought sanding it down would work. Perhaps the disc expands when hot or something changes. Well, I suppose I learned the lesson the hard way. I'm just curious if I can somehow salvage this, as it would cost me $200 more in angle iron to recut them, not to mention the couple more days.

My X length rail total is 4500mm,
1 X rail is sitting good at 27.5mm to 28.45mm
other X rail is sitting at 26mm first quarter to 28mm
My Y length rail is 1950mm,
Both Y rails are at 26mm +/- .5mm

Does anyone know if it would present any problems to have the rails at 24mm high rather than 28mm, and use 4mm flatbar to shim them up with?

Thanks for the info on the methods everyone. I'll definitely use a better method.

Cheers,
Chris

[Surfcnc]

Ok salvage it is.

There is no harm in making the rails and checking the fits yourself with out any packers. If necessary put in some packers should problems arise..

Some tolerances will change regardless.
1. the gantry / Y axis car will move towards the top of the rail
2. the swing plate mounted to the gantry / Y axis car will move away from the rail

Ross

[Gerald D]

The drawings used to show 25mm rails and they did work sort of okay.....

- The skate rollers need to miss the curved fillet inside the corner of the angle iron.
- When using small pinion gears the motor shafts can foul on the gantry ends
- the slots in the motor plates don't allow the motors to swing that far up

[litemover]

Thanks for chiming in Gerald. What if I place a 10 x 3mm flatbar shim under the rack? Will that space the swing plate far enough back into position ok? Suppose I could order more angle iron later on if this doesn't work... Not much to lose trying at this point.

BTW< what is everyone using to check the rail height across the entire rail? Gauges? I've been using my calipers and square.

[Gerald D]

A spacer under the rack is more trouble than solving the other implications will be. Simplest is a pinion size just bigger than minimum (if you plan on belts/gears anyway.). Otherwise a bit of local filing/grinding will get the motor plates swinging further up.

[litemover]

Thanks Gerald.

I have one X rail that teeters between 28.00 and 29.34. Am reticent to sand it further down in case I mess it up. Perhaps will just lightly sand the areas that are too high.

Out of the bad X rail, I can cut a segment out that would be 28mm long for one of the Y rails 2000mm long.

Which leaves me to only have to purchase one more 6m long piece of rail for $60 NZD. What I'm wondering is, would it be ok to weld together 2 pieces of angle iron to create a single Y rail 2000mm long for the other X rail, one piece would be 1500mm, and the other 500mm? Then cut and bevel that one down to 28mm as one piece? If this is the case, then this mistake would only have cost me $60.

Also, one other question, can I use M10 stainless bolts on the rail skate for height adjustment, instead of M12, as this will save me $40 in tap, 13/32 drill bit, and setscrew/nuts. The hole on the rail skate taps fine at M10, so was just wondering as this would reduce my mistake down to $20 (minus a few days work) while keeping a 28mm rail height.

Many thanks for all the help guys, She's coming along. Should have the table, gantry, and Y car finished early next week but not painted. Will redo the rails on the built table instead of on the ground.

Cheers,
Chris

[Surfcnc]

Sand down the high parts

No way ... deck the whole rail to a single height with a series of continuous actions along the whole length of the rail.
The high parts will get touched while the low parts will be left alone.
The final pass will lightly touch all of the rail ensuring a consistent height.

i'll leave the rest to someone else.

Regards
Ross

[litemover]

That is what I was trying to do with the other rails which brought them down to 25-26mm. Something must be wrong with my grinder when it gets hot. It's a bosch too.

[Surfcnc]

Could you show us a few pics of how you did it and or the jig you used.

Ross

[litemover]

Sure, just used the skate in the plans. Leveled out the bolts with a square and digital calipers. I used a sanding disc on top of a grinding disc. Will post photos when I get back to the shop next week.

[Surfcnc]

Chris

This is no mystery, carefully study the attached photo with me.

Sled.jpg

By just using four bolts, no matter how carefully measured for height, error creeps into the process.
The reason for this is that the bolts are very close to the disk itself.
They are clearly visible in this shot.

This jig provides an very large flat surface that controls any movement both left to right and back to front.

Also note that I have two melamine surfaces sliding over the top of each other.
This is to minimise the friction on the surfaces so that thay slide with a smooth action.

Looking at the pics of the rails you posted you have not been able to control some of the the front to back movement with just the four bolts sticking out of the top plate of the skate.
Hardly a surprise as the aspect ratio of the height of the bolts to the width is working against you.

By comparison the jig I have used supports the grinder over at least 3 times the distance front to back, let alone any calculation of the total surface area the jig bears upon.

PRACTICE

The next step is to make a jig, then practice on something non critical.
I know that sounds a obvious but so many rip into expensive materials with no previous experience then wonder why something has gone wrong.
That is exactly why those smug tradesmen with their lifetimes of experience laugh at a newbies trying to emulate their skill.

Good luck with your rails, you now know everything you need to know !!

Regards
Ross

[litemover]

Thanks Ross, I'll definitely make that jig and use it on the rails once I get the table up. I'm going to shift on getting the table up next week so I can have a higher surface to work on. Then I'll get the melamine boards to make the jig.

Thanks again for the tips.
Christian

[smreish]

http://www.mechmate.com/forums/showt...0&postcount=29

Previous production version of same idea....
Notice plastic PVC laminate on bottom of plywood sled for gliding

[Alan_c]

You dont seem to mention a cutting disk, are you using a cutting disk to cut the angle to the correct height or are you grinding it down with the sanding disk/grinder combo?

[litemover]

Found a great article on how to heat straighten beams without welding them, just with a torch. http://www.fhwa.dot.gov/bridge/steel/02.cfm#d. Going to try it tomorrow in my beams.

[KenC]

Actually, both are the same thing. I find welding is the easier way to apply heat...

[Surfcnc]

Chris great detail there.

Ross

[litemover]

It's a good paper on bending beams with heat, knowing any beam can be straightened with this method is a relief. Plus, I don't have to weld, or grind them out later. Should be interesting. I will try using the V method on my beams and my rails which have slightly bent.

Will continue with cutting rails later in the week.

[litemover]

Just a question about the support board. At the moment, I can get 2x 12mm 3660 x 1800 mdf. Can I glue those together for the support board material?

Thx

Chris

[Red_boards]

I'd say it's not a problem. I would use epoxy for glue.

You get to do this again when you glue the sacrificial layer on after bolting the base board to the frame.

PS there are some good suggestions in the forums about drilling through both sides of the base board cross supports so you can easily drill the base board, and for clamping the base board under the supports when drilling so that you get to work from above, rather than getting sawdust in your eyes, like I did.