Board Mill

[Barry Young]

How we got to where we are now:

When I started this project I had 15 years experience as a Journeyman Machinist on both conventional and CNC equipment and had been a CNC Programmer for three years in a furniture factory doing 2D work only. I had very little experience with electronics or building working machines. I also had no money. I did however have a Grizzly X2 Minimill and a 9X20 Jet Lathe and a shop full of woodworking machines.

Two years ago the decision was made to manufacture the worlds largest wooden cameras and accessories. I had a Grizzly minimill and decided to retrofit it with CNC equipment. The money was saved and the orders were placed. The equipment came, woo hoo! A Xylotex 4 axis driver box and four 269 oz/in stepper motors and a set of motor mounts and cheap single trace ball screws from CNC Fusion. The equipment was installed and a one year old relatively fast computer was moved into the one car garage to control it. Two days later when the Z axis dove for the table there was no way to shut it off because the emergency stop buttons had not been wired in yet. The cable from the box to the motor somehow got yanked in the confusion frying the Xylotex board. Saved for and bought a new Xylotex board then two days after receiving it, sent 35 volts into the parallel port on the computer while trying to find the correct power supply for the e-stop buttons frying the mother board. Saved for a new motherboard and installed it but now the computer wanted a replacement of the XP operating system because the motherboard had changed. More saving and got a new operating system. The ball screws were not the good Nook screws, but junk designed to transfer stuff from here to there, not designed to control a precise machine tool. The table was too small for the parts I needed to make anyway. I sold the CNC Fusion kit on ebay and kept the Xylotex box and motors then saved for a larger table from DeWayne Harlow at CNCBridges. After 4 months, 25 broken promises for delivery and an offer for half my money back, I contacted the authorities and received a full refund of my money but none of my four months of waiting were returned to me. All of this was the precursor to this thread. All of this saving, waiting, and getting screwed made me decide to design and build my own CNC milling machine/router/lathe from scratch.

The design phase:

I had built a workbench in my shop while waiting for the CNCBridges XY table. The bench is 72 inches long and 36 inches wide. A very nice sturdy table made from recycled wooden sheet metal pallets. All the joints are mortice and tenon and all of the frame members are solid hardwood. After deciding to make my own mill, using the workbench to set it on was a given. This defined the footprint of the machine. The first photo shows the sketch the bench was built from. This drawing details the joinery. The second photo shows the base of the bench assembled. The end frames are joined together by stringers. Thethird photo shows the base of the bench semi enclosed and waiting for doors. The frame and panel doors were made and hung and the top inlet and the bench was done. So Yay! had a bench.

Now that the footprint was written in stone and as large as my shop would accomodate, it was time to write a specification for the machine. A sort of design guidline of must haves. Because the parts I intend to make are very precise, I needed a machine with .0005 accuracy and .0002 precision. It needed a really long work envelope compared to other machines. More log shaped than cube shaped because more than 95% of what I intend to make will be from a board 1 inch thick or a sheet of brass 1/8 inch thick. The longer the better though because then I would be able to get more parts per blank. The machine has to be rigid because of the length of the X axis. This ruled out aluminum as far as I was concerned. Originally I had wanted to use aluminum, but I bought a heavy aluminum extrusion and tested it for deflection by supporting it at both ends and putting a weight in the middle while measuring deflection with an indicator. Aluminum was definitely out. A heavy wall square steel tube was similarly tested and found to be very much stiffer. The X axis needed to be as long as would fit and had to have a carriage wide enough to mount the Z axis on. Y axis would need to be no more than 12 inches of table travelling 12 inches. Z axis would probably have to be around 8 inches to accomodate long tools and one inch thick materials or the occasional tall job with shorter tools. Z axis turned out to be ten inches because of the geometry surprises that came later on.

[Barry Young]

I looked at thousands of photos of other peoples machines. I looked at the machines at work. Finally after seeing a photo of a DaVinci router made by Techno Inc., I knew I had found the basic design I needed. On this machine the gantry is rigid and the table slides under it toward and away from the operator. Because my X was so long compared to Y this made great sense to me. My needs were for a Y axis that could be controlled to precise limits and an X that would NOT flex despite its great length. This made a fixed gantry ideal because a fixed gantry can be supported by the lower frame in the middle and a moving one cannot. This rigidity was the driving force behind the design. That the finished board would be delivered to the front of the machine when finished where it can be unloaded without threading it through the opening between gantry legs was a plus but not a primary consideration. because the machine would load from the front and the table only had to be 12 inches wide, the total travel of the table only had to move 12 inches fore and aft. That made the base 24 inches wide and 72 inches long. Some calculations considering the width of the frame supporting the X axis, the height of the table on its ways and the length of the longest anticipated tool and the thickness of the thickest anticipated workpiece led me to believe that a frame 24 inches tall would be sufficient. 24 inches was not sufficient as we shall see, but it looked good on paper. Knowing that the base was 24 wide and 72 long and had a back that was 24 high allowed me to calculate the length of diagonal braces on each end. Then all that was left was to add three square tubes tubes for the Y axis to ride on and a total of four uprights in the back and I had enough information to order steel. The attached bitmap is a CAD drawing of the finished design.

It took two days to do the welding with the little Harbor Freight MIG welder I had at the time. All joints between members were welded all around as much as was accessable. The tubes as delivered are shown in the first photo. These tubes are 2X2 square tubing 72 inches long with 1/4 inch wall thickness. The tubes for the base are mitered at 45 degrees because we felt it would be easier for us to clamp them together at the corners. In retrospect it probably made little difference. The second photo shows making the miter cuts in a Harbor Freight horizontal bandsaw with the vise rotated 45 degrees.

[Barry Young]

Two of the 72 inch long tubes were laid across an old wooden table that we use for welding and hammering on. It is not very flat, but the tubes are pretty straight. These two tubes were there so that we could lay the short 24 inch Y axis support tubes across them and they would be flatter than if the were on the table top. What we are trying to do here is to create a plane for the short tubes so they will not be twisted when we weld the Long base tubes to them. Next the 72 inch front and rear base tubes are laid upon the short 24 inch Y axis support tubes. The long base tubes are clamped to the short base tubes with bar clamps. You can see this clearly in the first photo. The ends of the base tubes were squared up with a drywall square so that a rectangle would be formed rather than a parallelogram. I measured from the end of the tube destined to be in the back to where the center of each Y axis support tube should be then marked the long tube. Then I measured to the center of the 24 inch long Y axis support tubes as viewed from the end. This made it easy to line up the short tubes and clamp the long tubes to them. It is very important to line up your clamp pads exactly in the center of both tubes as they have a tendency to rock if you don't. The second photo shows a clamp viewed from above. Notice that the clamp nose is inside the end of the Y axis tube and the clamp screw is on the outside of the Long base tube. The long base tubes are now ready to tack, then weld to the Y axis support tubes as my buddy Bryce is doing in the third photo.

With the first five tubes in place, we were able to weld in the end tubes of the base at the miter joints as shown in the fourth photo. Now we had a base that was pretty flat, and it had three tubes welded to it which would eventually accept the linear ways for the Y axis.

[Oldmanandhistoy]

Hi,

Looks good so far

Will you be doing anything about the stress in the steel frame?

John

[Barry Young]

Originally Posted by Oldmanandhistoy Hi, Will you be doing anything about the stress in the steel frame? John

I will be using shims. My freezer is a tad small for this item.

Barry Young

[Barry Young]

Now that the base was done it was time to put a back on the machine. I laid the four 24 inch tubes for the back on the base where they would go if the back were folded forward. On top of these I laid the the 72 inch upper X axis support tube. Everything was clamped up and moved around until it was as close as I could get it to perfect then it was clamped up as in the first photo. The second photo shows the opposite side. Notice that only the short tubes that are clamped get weld this time. Next the lower X axis support tube was welded into place exactly as the upper one had been.

The back assembly was now tipped up into a vertical position and rotated 180 degrees so the X axis support tubes face the front of the machine. and was clamped in place as shown in the third photo. Notice that the ends of the uprights were located by clamping a board to the bottom of the lower frame and setting the upper frame on these boards as in the fourth photo to aid in getting the big pipe clamps in position. The fifth photo shows a diagonal brace which was clamped to both frames to hold the back 90 degrees to the base as set by a framing square. Photo six shows the frame clamped from the back, A board had been clamped across the first two uprights of the back to make room for the diagonal brace. Now the alignment of the X axis support tubes to the tops of the Y axis support tubes can be checked with an indicator as in photo seven. The height of the X tubes can be adjusted by tightening or loosening the clamps supporting the lower ends of the uprights. When everything was as perfect as we could measure, we started welding beginning with small tack welds on each end then filling evenly.

This completed the frame. Now just fillin all the welds that look so bad because we are both machinists not welders and we had insufficient equipment. Then we carried the frame into the workshop where it will now live.

[Barry Young]

The frame was hauled inside the shop and set on the workbench as in photo 1. It was decidedly ugly so it received a paint job and looked a little better in photo 2.

It was at this point that I realized that the X axis support tubes were much too close together to offer resistance to tool pressure fore and aft. It had looked good on paper, but there was no doubt that the X axis support tubes were much too close together. I was going to want twelve inches between the X axis ways. The realization was awful. Then an inspiration. Off to the steel supplier for a 1/2 inch steel plate 12 inches wide and 72 inches long. This plate was bolted directly to the X axis support tubes with 72 socket head cap screws counterbored into the 1/2 inch plate. I also drilled and reamed for two 1/4 inch dowel pins in case I ever wanted to remove the X axis to reduce the weight for transport to another location. Work started progressing so quickly that I forgot to take pictures.The heavy plate was aligned with the tops of the Y axis support tubes using a dial indicator just as the X axis support tubes had been when the back was welded on.

I took the base off of my Harbor Freight $39 bench model light duty drill press. Then I removed the belt cover. Then taking the table off and turning it upside down allowed me to clamp the drill press to the 1/2 inch thick plate and lower the head to the work. This worked very well indeed.

The ways were originally going to be one inch aluminum rods bolted with stand off bolts like the Thomson linear slides except aluminum rather than steel. I had intended to build adjustable acetal block bearings to slide on these rods. After much thought and weighing the advantages versus price, I decided that with this much investment in labor, materials and time, I had better just buck up and use the best materials I could get. So it was to be recirculating ball bearing linear slides with trucks from THK, IKO or one of the other suppliers. Of course being less than wealthy I would have to buy them used on ebay. I began to buy slides and rails. Much homework was done reading everything on CNC Zone about linear rails, trucks, brands and how to mount them. The first set that came up on the radar was a set of four THK HSR25 trucks with 24 inch rails. Well, that would satisfy the outer ways for the Y axis so I sniped them. They were beautiful, heavy duty and appeared rugged. After that first set arrived via UPS, I was so impressed that I decided to go with HSR25's for the entire project. I had already purchased some IKO slides that were in new condition but too short even for Z axis, so it was an easy decision to standardize.

The problem was that 72 inch rails are very rare beasts on ebay, and when they do come up, they go for way more than a poor guy like me could afford. I waited for weeks and finally an acceptable set showed up. They were 74 inches long and came with four trucks. They were only 20mm not the 25mm I wanted, but they would have done the job. I set up my darkroom clock and synchronized it with ebay time so I could confirm my bid in the last 5 seconds. The bidding was fast and furious in the last two minutes. The price jumped from $80 to $270 before the clock reached one minute remaining. I entered a bid of $551.11 and waited for the seconds to tick down to 5 before confirming my bid lest another bidder see my bid and have a chance to revise his. The auction ended and I had lost the auction to some joker who was doing exactly what I had been doing but had deeper pockets. Heavy sigh. Now I was truly screwed. Rails that long are rare beasts and I did not want to butt multiple rails together knowing that single rails in that length were available. I just hate waiting for stuff I need to come up on Ebay so I emailed the guy who appeared to be selling more rails than anybody else on Ebay hoping he might have some he had not listed yet. No word for a week then an email came stating that he thought he had some but needed to check his warehouse. I want a warehouse, that sounds cool. A week later he emailed that he had two HSR25 rails that were 72 inches long and offered me a very reasonable price because he had no trucks. He set up a special auction on ebay for me with a buy it now option and told me the auction number and what time they would appear. I could barely sleep the night before and set my alarm for two hours before the auction so I would be sure to have coffee in me before the auction started. The auction lasted exatly 30 seconds and I had finally made arrangements to receive the hardest to find piece of the puzzle.

I still needed 10 trucks, 4 for X, 4 for Z and 2 for the center rail on the Y axis. The next set of goodies that showed up were a pair of 32 inch HSR25 rails with four trucks. These would work for the Z axis but would need to be shortened. I won them easily because now I was truly a motivated buyer bidding wildly too much for things to get this whole gathering process over with. Next a set of brand new in the sealed boxes wide trucks came my way for a song because they had no rails. These would be perfect for the center Y rail. Now all I needed was one more 24 inch rail and four more trucks. Those showed about a month later. The gathering was mostly done. Now I could start thinking about finding ball screws.

At this point the long X axis rails arrived on a brown truck. Upon unwrapping them I was immediately happy I had bought these rails from Mr. Warehouse. He had screwed the rails to a 1X4 pine board with drywall screws, then wrapped them securely with bubble wrap and stuffed them into a cardboard tube. Very nice shipping technique! Nothing bent or broken.

[Barry Young]

I decided to make the lower X rail the Master rail. From this one rail everything else was aligned. I carefully drilled and tapped the 36 holes using the rail itself as a drill jig. To get the fasteners centered in a rail 72 inches in length is not such an easy task if you are trying to do it by measuring. So I did not measure. I got the rail aligned within .0005 inch to the tops of the Y axis support tubes and clamped it in place then re-checked. The first drill used barely fit in the bolt hole in the rail. Using a cordless drill, I used it to drill a dimple into the 1/2 inch steel plate that would be supporting the X axis rails. I followed this drill with a #7 tap drill for 1/4-20. The hole was tapped thru without removing the rail. I repeated this on the other end after once again checking to see that the rail was parallel with the tops of the Y axis support tubes. Once the Master Rail was in place, it was relatively easy to bolt in the slave rail for X parallel to the Master rail.

[Oldmanandhistoy]

Originally Posted by Barry Young I will be using shims. My freezer is a tad small for this item. Barry Young

I have heard about stress relieving and how the frame can move over time because of the stress but as yet I have not looked into it in detail. I thought you may be able to take the frame somewhere to have it done.

So from your response I’ll take it you will not be stress relieving. Do you have any idea how much the frame can move; are we talking fractions of an inch? I would like to build my next CNC router frame from steel tube so any information would be helpful. Of course I will be searching this website and the net for more information so if you don’t have the time to reply that’s not a problem.

Thanks so far for taking the time to post your build in such detail; I will be following it with great interest.

John

[Barry Young]

Originally Posted by Oldmanandhistoy I have heard about stress relieving and how the frame can move over time because of the stress but as yet I have not looked into it in detail. I thought you may be able to take the frame somewhere to have it done. So from your response I’ll take it you will not be stress relieving. Do you have any idea how much the frame can move; are we talking fractions of an inch? I would like to build my next CNC router frame from steel tube so any information would be helpful. Of course I will be searching this website and the net for more information so if you don’t have the time to reply that’s not a problem. Thanks so far for taking the time to post your build in such detail; I will be following it with great interest. John

Hi John:

I am fairly certain that anything this large would be a problem to get into a heat treat oven. This is because right now all the airplane manufacturers are up to their ears in orders. Lots of aircraft parts are large. Most large aircraft parts get some form of stress relief and or heat treatment. They have been hogging all of the large heat treat ovens for about 8 months now. If you could find a company that would stress relieve a large weldment, the cost would be enourmous and way beyond my means. I think it more prudent to build the thing then later if a part goes wonky shim it to make it work. I have not seen weldments move much after they are complete. I am no welder, but I believe stress relief in weldments is mostly to help with distortion that creeps into the weldment as a result of the large amount of localized heating that occurs during welding rather than to correct distortion from time. This belief could be a bunch of Hogwash too because of my limited experience with this technique and with welding.

Barry Young

[Barry Young]

As soon as both X rails were in, I slid the trucks on. What a feeling, it did not matter how hard I pushed them into the rail, they still slid easily. What a great product.

A magnetic base attached to one of the trucks on the Master rail holding a tenths indicator allowed me to run the indicator against a straight edge that was bridging the Y axis support tubes. By loosening a bolt here and there and with light taps from a rubber mallet, I was able to get the Master rail parallel to the straightedge within .0002 inches when measured over 68 inches. For my purposes that is close to perfection.

Next I made a temporary X axis carriage which was bolted to the trucks on the Master X rail and which had one bolt into one truck on the Slave rail. I loosened every bolt in the slave rail then moved the carriage along the rail in two inch increments and as each bolt was exposed it would be tightened. This effectively made the slave rail parallel to the Master X rail.

The next step was to saw out a piece of 1/2 inch thick MIC 6 cast aluminum tooling plate (Take the deed to your house when you go to buy this stuff) for the X axis carriage. This is being done in the first photo. Luckily I found some Mic 6 at a surplusser that had a small amount of corrosion for a very attractive price. 1/2 inch aluminum cuts great on a table saw with a carbide woodworking blade, you just have to feed it slowly.

I cleaned up the edges with a file and then stoned the faces of the plate. The bolt holes were eyeballed for center of holes on the trucks with the plate sitting on the trucks, then the lines were extended with a 12 inch engineers square. The holes were drilled with a largish clearance drill that would give room for the 6mm bolts to have about .020 inch slop. These holes were then counterbored 7/16 to leave a large counterbore around the attach bolts.

[Barry Young]

Because the trucks for X and Z overlapped on opposite sides of the X axis carriage (the Z axis carriage has the rails attached to it rather than the trucks), very careful layout was required to enable the trucks to be bolted to the carriage without interfering. In fact, you have to put one of the bolts into each Z axis truck before you can attach the X axis trucks since once they are attached, there is no room to get the bolt in past the X axis trucks.

The plate was blacked up with a Marks-A-Lot Pen, carefully laid out, and then the thru holes and counterbores were drilled for the X axis trucks. Then the thru holes only for the Z axis trucks were drilled slightly oversize to allow for adjustment. The plate was then flipped over to counterbore the holes for the Z axis truck mount bolts. The Z and X axis trucks were then lightly bolted to the X axis carriage and installed on the X axis rails. The X axis trucks were then tightened and to my surprise the X axis no longer wanted to move.

Because the X axis rails were bolted to a 12 inch wide piece of hot rolled steel, they were not co-planar. The solution was to lay the carriage on the X axis trucks, then measure with a feeler gage to see how much shim was required to allow the carriage to be securely fastened without putting a twisting load on the trucks. This required a bunch of shim. I had very little on hand and wanted to have shims that were wider than the normal feeler gage stock I could put my hands on right away. So I made shims, here is how I do it.

Take a soda can and cut off both ends. Cut it up the middle to make a sheet. Soda cans are very tightly controlled for thickness at .005 inch. I use a paper trimmer to make them square with nice sharp edges. Because the shim is now a curved tube, I turn it label side down on a corner and drag it across the corner of the bench or whatever, this makes a nice flat piece of stock I can cut the shims from. See photo 1. This sheet of shim was cut up into pieces that would fit between the bolts on the trucks. Once the shims were installed several times to get it right, the carriage moved freely when bolted up tight. My girlfriend Deborah ensures that I have a limitless supply of .005 shim.

Another piece of plate was cut on the table saw for the Z axis carriage. The X axis carriage was removed from the machine. The Z axis Master rail was attached to this carriage by first drilling and tapping one hole for one bolt in the end of the rail. The plate was then made parallel to the rail and the hole in the other end of the rail was used as a drill jig to drill and tap the second hole locating the Z axis Master rail parallel to the edge of the carriage. The rest of the holes were then drilled and tapped and bolted.

The slave rail was slid into the slave trucks and then I was able to drill and tap knowing the slave rail was automatically aligned by the trucks. No shim was required when mounting rails to the tooling plate, just HRS I guess.

The X and Z axis carriages were now complete. Y would have to wait until the X and Z ball screws were installed because I only wanted to have to stand this machine up once.