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oskar270
01-11-2013, 03:24 PM
I need to purchase 6 aluminum pieces each approx. 1/2" x 6" wide x 48" long and both edges of these pieces must be perfectly straight. The choice I have is either aluminum flat bar which is an extrusion and the edges are not always perfectly straight or aluminum plate which is cut to size with some kind of a band saw and the edges definitely are not straight (tolerance is always +1/8").

A local machine shop will charge me about $50 per piece to make the edges straight + one time setup cost of $75 + tax. I find this cost very high and therefore I will do it myself.

I did use my router before to cut 2 slots on 1/2" thick aluminum each 3/8"x8" long and it did a good job (see attached pics) so I was thinking to make a jig as per attached picture and trim the edges myself

http://s285.beta.photobucket.com/user/kolias/library/Aluminum%20Trim?

On the picture, the vertical left piece of MDF / plywood will be the guide for the router. The only real challenge I see is how to get both edges perfect parallel.

Do you see any problem with my jig? Suggestions?

Toolguy
01-11-2013, 03:43 PM
Do you have a mill?
If you're going to use a router jig you don't want the router trapped between the guide and the part. That will lead to gouges and all manner of problems. Gage the router and the part off the same vertical surface. You can make a spacer board to go between the router and the upright to get the width you want on your aluminum. You can clamp the part and spacer to the table on the ends to keep them in place.

goose
01-11-2013, 04:00 PM
Do the edges need to be parallel as well as straight?

Have you considered a woodworking jointer? I don't see HSS knives having any problems with AL, provided the proper safety procedures are followed.

edit: Sorry, missed the part about must be parallel. I think your jig would be fine, but I don't know what tolerance you're aiming for.

thistle
01-11-2013, 04:39 PM
I just cut a bunch of aluminium plate and the whole lot has warped in every direction, dont assume that if you cut the plate it is going to end up straight.

kevbo
01-11-2013, 04:58 PM
I had some serious warping issues with some 1/2" 1005. We were H2O jet cutting ~2' x 4' pieces out of 4x12' stock and they were cupping by 1" in some cases. Were able to press them down flat enough, but still nowhere near flat.
When I say we, I mean the shop with the big-ol water jet we hired to do the work. They were warping enough to catch the nozzle and break it off! Sometimes the simple jobs give the most trouble!

If you get cast Al annealed tooling plate, it doesn't warp hardly at all. Soft and kinda sticky to machine, doesn't hold threads very well, but it is stable enough.

Black_Moons
01-11-2013, 05:00 PM
Put a guide on one side, have plate rest against guide and router be on other side of plate from guide. Add a small spacer between router and guide

Route one side as flat to the guide as you can. Flip plate over. Remove spacer, Flat cut edge of stock is now resting against flat edge of guide, Do another pass to bring the other side in alignment with the first

Mcgyver
01-11-2013, 05:14 PM
I need to purchase 6 aluminum pieces each approx. 1/2" x 6" wide x 48" long and both edges of these pieces must be perfectly straight.

Perfect isn't obtainable - what do you mean by perfect, .0001", .001, .005, 1/16" etc. What did the machine shop say they could do?

Getting large pieces straight/flat to a high degree of accuracy is very difficult.....but you need to define what a high degree of accuracy is

Fasttrack
01-11-2013, 05:28 PM
Perfect isn't obtainable - what do you mean by perfect, .0001", .001, .005, 1/16" etc. What did the machine shop say they could do?

Getting large pieces straight/flat to a high degree of accuracy is very difficult.....but you need to define what a high degree of accuracy is


Just what I was going to say!
In my experience, extruded aluminum bar is every bit as straight/flat as the MDF you are using as a guide... especially with a round router base. It will follow any knicks or bumps in the MDF.

oskar270
01-11-2013, 05:53 PM
Thank you all, lots of good info here

No, I don’t have a mill and the tolerances I'm after is about .001. BTW my aluminum is 6061 and I will be using a 4 flute carbide end mill for this job

The machine shop said they will shave both edges to be straight and parallel; no doubt they will do a good job but the cost is very high and I'm sure I can do the same job and at the same time get the experience for similar operations later on. As you can see from the attached pics in my 1st post, the slots turned out much better than expected.

If I order my pieces in plate they are perfect flat but the edges are not straight enough since they cut the pieces I want with a saw from a bigger plate. If I order extrusion, chances are that some will be good and some they may be warped. So its better to get the plate and the cost is only about $10 more per piece

Black_Moons I like your idea and was thinking along similar lines

macona
01-11-2013, 05:57 PM
I have used a jointer on aluminum and it worked great. Almost a mirror finish.

Bob Fisher
01-11-2013, 06:39 PM
I would bet that, if, you had a way to check the edge of the MDF, you would be disappointed in hoping that will produce a .001 tolerance. Parallelism will be more difficult even. Not trying to be pessimistic, but .001in over a 48in length is not easy, even for the machine shop. Bob.

Mcgyver
01-11-2013, 06:57 PM
. Not trying to be pessimistic, but .001in over a 48in length is not easy, even for the machine shop. Bob.

+1......whats the piece for? application?

Fasttrack
01-11-2013, 07:01 PM
I would bet that, if, you had a way to check the edge of the MDF, you would be disappointed in hoping that will produce a .001 tolerance. Parallelism will be more difficult even. Not trying to be pessimistic, but .001in over a 48in length is not easy, even for the machine shop. Bob.

What he said.

Do you really need 0.001" tolerance? As I said, the extrusion will be as straight as the MDF. If you are worried about it being warped, any chance you can flatten it out? What tolerance do you need in the other plane?

darryl
01-11-2013, 08:14 PM
Comes to mind that you will need a guide that's at least that straight- that's the first, and a significant challenge. I have found that extruded flat bar is pretty good, though you do have to check to make sure you haven't got a piece with a kink in it. Once you have a guide that's accurate, the rest is setup and control. So, where to go from here- what's the straightest edge you can find?

My recently finished taut wire straightedge shows my piece of flat bar being out by just under 3 thou over the 5 ft length- I haven't yet tried to correct it. It's possible that by selecting a piece you could get one of that length that's within 1 thou- but the shop will have to be willing to let you do the checking, and you'll need an instrument of some kind to do it. Or- they may be able to select a piece for you. Short of that, it's possible that a piece of anodized aluminum door frame material might be 'straight'. The edge of a sheet of plywood, mdf, or similar- maybe but probably not, and there will be random deviations that exceed that limit. A good, straight edge is not that easy to find.

Bob Fisher
01-11-2013, 08:21 PM
The more I read, the more curious I become. What is the application, and why does it need to be that accurate? Bob.

oskar270
01-11-2013, 08:57 PM
I'm retired and building CNC's as a hobby. This link

http://s285.beta.photobucket.com/user/kolias/library/4th%20Aluminum%20CNC?

shows my last cnc which I built last summer and it was sold a couple of weeks ago. It's not a money maker hobby but rather I enjoy the work and the challenge, then work on them a bit and then its time to make a new one which is always better than the one before. The last pics on the link shows where the 6 pcs will be used, it’s the base of the cnc and this table top is 26"x40"x3/8" thick plate. For the base I used extrusions and had a hard time to level the table top because the edges were not perfectly straight (they had highs and lows, not a lot but enough) and so I used shims. Not a big deal because it came out perfect. For the gantry + X & Z axis I used plate

The only tools I have is a table saw, Delta bench mounted drill press, Chop saw for cross cuts with an aluminum blade, recip saw with metal blades, skill saw and scroll saw all using metal blades and an old cheap router. I do the work in my garage and part of the challenge is to do any task with the tools I have because space is limited. I have modified my drill press and can drill the edge of a 48" long piece as precise as any machine shop.

.001 accuracy is not a fixed number. I was thinking if I can run my router to shave the edges a bit, then it will be perfect and even if I have to use some shims it should be much easier than before. The emphasis is on the safety and having both edges as parallel as possible

Scottike
01-11-2013, 09:21 PM
.001 in 4' seems like a pretty tight tolerance to me.
My thought would be to rough cut each piece slightly oversize
on a table saw with a carbide blade and then (Carefully) finish each piece
with a pass or two with a router guided by a milled steel straight edge and
hope for the best.
or you could always scrape the edges.

edit: Missed a couple of posts while I was typing.

oskar270
01-11-2013, 10:22 PM
I do have a very good straight edge. It is an aluminum extrusion about 6ft long, 1.5"x1.5" and it was the track in one of the windows in my house where the blind rollers used to ride. I used to have more when I replaced all the blinds in the house but I use them all in various projects and just kept the 6 footer one

Paul Alciatore
01-11-2013, 11:30 PM
If I were designing such a machine under your limitations, I would consider purchasing some flat ground stock for use as the rails. Smaller pieces, perhaps 1/4" x 2" x 4' could be bolted to the tops of your aluminum sides. They would provide the precision straight edges needed while the aluminum provided the stiffness. A bit of alignment would be needed but it should be more accurate than depending on a piece of MDF. I don't see why you need the two sides parallel, but if you do, you can achieve that with a 6" caliper while bolting the ground stock on the aluminum.

Another approach would be to generate the straight edges with abrasive mud between pairs of the aluminum pieces. Cut them a bit oversized and lay them side by side on a piece of the MDF with some abrasive compound between the touching edges. Press them together and rub back and forth with 6 or 8 inch strokes. Altering three of them A-B, B-C, and C-A as well as swapping ends while doing one pair should quickly bring the three edges straight. More could be added to the rotation or just do them in threes. Measure the widths as you go and bring them down to the 6" and parallel by suitable adjustments in the pressure while lapping. This procedure would make edges that are far straighter than any MDF will ever be.

You will have to watch out for expansion/distortion from the heat of your hands. Perhaps a wood handle could be fashioned to grip them.

darryl
01-11-2013, 11:57 PM
Clamp the straight to a piece of plywood or mdf, making sure to clamp at least two places in the middle, ie use four or more clamps. If there's any need to take a bow out, do it as part of the clamping.

Make a base for the router which has at least one straight side. This side will slide along the clamped edge. Make the thickness of this base the same as the piece you're edging, and make the base to come only about halfway across the router. In other words, the piece you're trimming doesn't get interfered with by this temporary router base. Figure out the distance from the router bit to the fence, and then make two spacers of this length, minus about 5 thou. These spacers are used to position the piece you're trimming. You should then be able to slide the router along, trimming one edge of the piece. Run it at least two more times, always keeping the base tight to the fence. You might want to add some shims to the spacers so you don't have to take off 5 thou in one go. Only take off what the router can do without slowing down.

Now make two more spacers, length equal to the first pair plus the width of the workpiece. Put those in place, then secure a block at the end of each one. Remove the spacers, put the freshly milled side of the workpiece against these blocks, clamp down, run the router. It should just touch- probably miss in a few spots. You then unclamp the piece and use shims again to position it closer to the router. The router should take off an amount equal to the shim thickness. Judge for yourself how much can be taken off without slowing the router. The easier the cut, the less chance there will be for anomalies.

Do not under any circumstances run the router in a direction in which it will propel itself along the gap between the fence and the workpiece. This will almost certainly appear in the evening news as a shop accident.

In any event, the edges you trim will have the same curve, or lack of curve that your fence has. With luck there is no curve. The degree to which the spacers have been made exactly the same length will determine how parallel the finished edges are on the final product. Be sure to control burring so it doesn't interfere with your positioning of the piece against the spacers.

The straight-edged base that you make for the router will average out some of the roughness as it slides along, so your positional accuracy of the router will be enhanced. Trying to use the side of the existing round base will be a disaster- don't be tempted to do that.

Boostinjdm
01-12-2013, 02:06 AM
The aluminum bar stock that I've purchased in the past has been more straight over a long length than anything I can produce. I even own a mill....

oskar270
01-12-2013, 08:09 AM
The aluminum bar stock that I've purchased in the past has been more straight over a long length than anything I can produce. I even own a mill....

Its true, most of the pcs I get are good but there are a few which need some work

oskar270
01-12-2013, 08:23 AM
If I were designing such a machine under your limitations, I would consider purchasing some flat ground stock for use as the rails. Smaller pieces, perhaps 1/4" x 2" x 4' could be bolted to the tops of your aluminum sides. They would provide the precision straight edges needed while the aluminum provided the stiffness. A bit of alignment would be needed but it should be more accurate than depending on a piece of MDF. I don't see why you need the two sides parallel, but if you do, you can achieve that with a 6" caliper while bolting the ground stock on the aluminum.

Another approach would be to generate the straight edges with abrasive mud between pairs of the aluminum pieces. Cut them a bit oversized and lay them side by side on a piece of the MDF with some abrasive compound between the touching edges. Press them together and rub back and forth with 6 or 8 inch strokes. Altering three of them A-B, B-C, and C-A as well as swapping ends while doing one pair should quickly bring the three edges straight. More could be added to the rotation or just do them in threes. Measure the widths as you go and bring them down to the 6" and parallel by suitable adjustments in the pressure while lapping. This procedure would make edges that are far straighter than any MDF will ever be.

You will have to watch out for expansion/distortion from the heat of your hands. Perhaps a wood handle could be fashioned to grip them.

The 6 pcs which make the cnc table base need to be as straight as possible otherwise nothing mounted on them will be straight. I like you idea with the flat ground stock but I found the flat sides of my aluminum to be good and the main problem I have is with the edges on some pieces.

Never used abrasive mud before but sound like a good idea

oskar270
01-12-2013, 08:48 AM
Clamp the straight to a piece of plywood or mdf, making sure to clamp at least two places in the middle, ie use four or more clamps. If there's any need to take a bow out, do it as part of the clamping.

Make a base for the router which has at least one straight side. This side will slide along the clamped edge. Make the thickness of this base the same as the piece you're edging, and make the base to come only about halfway across the router. In other words, the piece you're trimming doesn't get interfered with by this temporary router base. Figure out the distance from the router bit to the fence, and then make two spacers of this length, minus about 5 thou. These spacers are used to position the piece you're trimming. You should then be able to slide the router along, trimming one edge of the piece. Run it at least two more times, always keeping the base tight to the fence. You might want to add some shims to the spacers so you don't have to take off 5 thou in one go. Only take off what the router can do without slowing down.

Now make two more spacers, length equal to the first pair plus the width of the workpiece. Put those in place, then secure a block at the end of each one. Remove the spacers, put the freshly milled side of the workpiece against these blocks, clamp down, run the router. It should just touch- probably miss in a few spots. You then unclamp the piece and use shims again to position it closer to the router. The router should take off an amount equal to the shim thickness. Judge for yourself how much can be taken off without slowing the router. The easier the cut, the less chance there will be for anomalies.

Do not under any circumstances run the router in a direction in which it will propel itself along the gap between the fence and the workpiece. This will almost certainly appear in the evening news as a shop accident.

In any event, the edges you trim will have the same curve, or lack of curve that your fence has. With luck there is no curve. The degree to which the spacers have been made exactly the same length will determine how parallel the finished edges are on the final product. Be sure to control burring so it doesn't interfere with your positioning of the piece against the spacers.

The straight-edged base that you make for the router will average out some of the roughness as it slides along, so your positional accuracy of the router will be enhanced. Trying to use the side of the existing round base will be a disaster- don't be tempted to do that.

I think I like you idea Darryl but have some difficulty grasping it properly. Is it similar to the first picture on this link?

http://s285.beta.photobucket.com/user/kolias/library/4th%20Aluminum%20CNC?

Mcgyver
01-12-2013, 09:04 AM
I do have a very good straight edge. It is an aluminum extrusion about 6ft long, 1.5"x1.5" and it was the track in one of the windows in my house where the blind rollers used to ride. I used to have more when I replaced all the blinds in the house but I use them all in various projects and just kept the 6 footer one

by very good, do you think think this extrusion is straight to .001" over 4'? In this craft you just can't make assumptions like that. Without some quantified reason, there is no way I would expect an extrusion to be that straight or for that matter better than bar stock.

Its going to be very difficult to machine something to that tolerance and you're not going to get it pulling the house apart :). Ideally to machine it you need an accurate machine with 4' of motion. I can't see a fence system or approach of unclamping and moving the work reliably holding a thou over 4'

might have to learn how to scrape :D



.001 accuracy is not a fixed number. I was thinking if I can run my router to shave the edges a bit, then it will be perfect and even if I have to use some shims it should be much easier than before. The emphasis is on the safety and having both edges as parallel as possible

The problem is that you don't know what tolerance you need and that its something that is somewhat difficult to quantify. Not many home shops will even have the equipment neccissary to quantify the straightness - ie 4' surface plate. By whatever technique you use, how are going to know? You don't know how straight the AL extrusion is off could be say .005" - then you'd ge checking against something with an unknown error.

The first thing you need is a way to check for straightness. It's meaningless to talk of tolerances if you have to way of knowing what you've got. Get a big used surface plate or camel back if you're serious or perhaps get the help a machine shop with one. As I said, really flat and straight over any lenght or area is a big deal, its takes $ and effort. A crude facsimile would be pay the machine shop to do one, watch them quantify it on a surface plate with feeler gauges or indicator and then use that as a check.

What did you use before and did that work well? As per above, quantify that - then you'll have a sense what tolerance you need.

RussZHC
01-12-2013, 09:25 AM
Few thoughts...how accurate was the previous CNC you made? I think I would have used previous machine to make parts for next machine (if I understand the process correctly, its the iteration thing, each "next one" getting better than the one before). From what you have said, you are wanting to make this machine better (more accurate?) than the previous, so, to state the obvious, improve the methods used. Which is what I assume this thread is about. It is possible you have reached the limits of accuracy with what is available to you.


Probably does not help you any but I am thinking rather than doing each piece one at a time, if you can solve straightness of guide problems, to do them as a "gang". What I am really thinking of is having all the pieces on edge and run through something like a machine shop bed grinding process. Could something be done on a woodworking thickness planer? Jointer?

I am making an assumption here you don't want to be messing with shims on the complete project? As opposed to being fine with using shims as part of the set up for trimming the edges.
Just asking since the two metal working machines I own both use fine shims at some point, to either help level them or within the body of the machine itself. "Absolute" is tough to attain, more so the longer the run.

vpt
01-12-2013, 09:37 AM
^ Thats what I was thinking. Use the old (last built) cnc to make the parts for the next.

RussZHC
01-12-2013, 10:04 AM
OP may find this thread of interest: http://www.cnczone.com/forums/linear_rotary_motion/101234-has_anyone_tried_using_thk_etc_rails_structural_el ements_machine_datum.html

more or less some discussion about using "off the shelf" parts from linear motion, not so much that but much of the discussion by necessity revolves around accuracy of rails as example.

Went wandering through some of the linear motion online catalogs, companies that really know this field and several things become evident.
The most precision can be easily changed.
Installation becomes vital, type of load can mean those wonderful straight rails go out of tolerance (or rather the position of the load can/will), certain finishes like hard chrome may not be able to be used at the most precise tolerances I assume because they are not then accurate enough. In most cases regardless of class of precision, there are limits as to length of individual pieces after which a butt joint is needed which means tons more details on how to make said joint accurate.

Not saying it can not be done, rather there are problems encountered and those companies have solved as many issues as possible I am sure.

To put the need of OP in perspective for me, that tolerance is about what polished and ground shafting is to approximately 2" diameter...I think it was Paul posting earlier...you are entering the "zone" where things like heat begin to effect measurements, cleanliness becomes vital etc.

oskar270
01-12-2013, 05:57 PM
Mcgyver you have good points and I thank you. My straight edge is straight because I have used it many times for different tasks and it has been always accurate for my needs. As I mentioned, I used extrusions before and they did a good job but had to spend the time to play around with shims and so I think if I could shave the edges of my extrusions it may be much better (less shimming). Tolerance "numbers" are not important for me because I donít have the proper equipment to measure neither I want to buy them. But I do have some basic measuring equipment and after I do a cut with the cnc I can see if my cut is ok or not and then I use shims to correct the problem and it always works.

Russ you also have good points and I thank you. All the cnc I built before have been very accurate and solid. How accurate? Well I did not measure it but all I know is if I cut a 20"x20" square or a 2" circle and measure the cut they are exactly 20"x20" or 2" diameter and the depth of cut is exactly as per my settings (1/8" or 1/2" or whatever my setting is). Perhaps I'm working backwards but I find it much easier to build the machine the best I can and then after I start my cuts make adjustments as needed. There is no way to make the parts for my next cnc because it takes me 4-6 months to design on paper the next one and by that time the cnc I have has been sold. This is a hobby work and I donít work on it continuously so it takes time to come up with a new design. Also you are right and that is my point, no matter what machine you have they always use shims in one place or another and I do the same.

Also I know about this thread on your link. Perhaps I'm wrong but I have been very happy with the linear rails and ball screws I buy from China and have never noticed any defects. When I started on cnc building I first checked on US manufacturers but their cost was way out of my reach. Then reading on the cnczone forum I found that others had been successful with these parts from China and so I gave them a try. For example, on my last cnc the cost for all the linear motion equipment was $760 including Fedex shipping and the same items from US manufacturers was $7,200 + shipping, a HUGE difference. Granted perhaps their material is made from some exotic metals or something but the ones I get from China to me look and behave like a very good quality product.

Also we should not forget that my cnc's are not for heavy industrial use on steel etc but rather for small scale commercial / private applications like wax or foam making, wood sculptures, sign making etc. I donít say that the US made equipment do not worth their money; just they are for different application

darryl
01-13-2013, 02:28 AM
Oskar, my idea is similar that pic, but it differs in some important ways. First, the base on the router is removed and replaced with one that would be about 8 inches long and about 3 inches wide or so. At the center of one edge, a half circle notch is created. When it's bolted to the router, the notch is centered around the cutter, not touching it. When the thickness of this temporary base equals the thickness of the workpiece, the router will sit vertically with no tendency to rock, and it will slide along the guide with no tendency to rotate. These are the two important things that are dealt with to start with, which aren't evident in the pic.

Secondly, the spacers I referred to also reference from the guide, which means that the edge of the workpiece that is presented to the cutter is parallel to the guide. In your drawing, the edge that the workpiece is referenced to is opposite the guide. It would have to be very carefully positioned and secured to make sure that you don't end up tapering the workpiece.

The longer set of spacers that I referred to are to position a couple of blocks that act as the second guide. These do require very careful positioning, but also give two secure points to reference the workpiece from (using shims), which eliminates any incongruities which might interfere with the exact positioning of the workpiece. If that was one long guide edge, it would have to be exactingly straight in order to do the job properly. Of course, your main guide has to be pretty darn straight to start with.

Note that when the cutter is set to be able to trim the full width of the edges, it will also be digging into the plywood sheet that everything is set up on. It might be a good idea to run the router across first to create this relief groove before clamping the workpiece and edging it.

One other thing- the finish left by the router bit may not be as smooth as needed in the final application. Chances are a spiral cutter will leave a better result, or you could arrange to do some smoothing another way.

oskar270
01-13-2013, 09:04 AM
Thanks for your time Darryl

I have revised the setup and is the first picture here

http://s285.beta.photobucket.com/user/kolias/library/4th%20Aluminum%20CNC

Did I get it right?