[Zach_G]

I heard my name so I guess I'll weigh in. Don't worry about machining the ballscrew ends, with a good carbide insert and stiff tooling setup you should be able to get through the case hardening which gets a lot softer in the middle. I had to do that with my cheap chinese screws which needed rework since they machined them to the wrong length. I've also heard of many machinists heating the end with a torch to temper down the heat treat.

Speaking of those Chinese screws, I got 20mm dia (also available in 25mm) and they are the first thing I would change. The single nuts have about 0.0025" backlash and the angular contact bearing blocks required substantial tweaking to get them acceptable. Could be fixed with a second nut but I think you'll be much happier with your ground screws as they also have better positional accuracy. That said if you end up not using them I'd be happy to take them off your hands! Due to the high lead of your 25mm screw its hard to say whether it will be more rigid until you compare datasheets and do some physical testing to verify the 20mm's aren't worn down.

Looking over your thread you got a good start. Love the custom spindle, I want one! I definitely agree you'll want to put some kind of additional bracing in your tubes for torsional stiffness whether that be ribbing, cross braces or the E/G fill like I used. Dave DecCausin's machine only has like 7" of Y travel which is how he gets away with much smaller tube sections. Finally, design in some extra Z height. I've got 14" and when you start stacking up the vice, part, drill chuck and good size drill bit you run out of space quick. I wish I had more like 18". It's not going to add much weight or cost for a few more inches.

[handlewanker]

Hi all, that's one of the advantages of a bolt down column, you can add a spacer to jack the height up and take it out if you want to get down for more rigidity.

My Ajax mill, (similar to a Bridgeport), has a 100mm spacer on top of the column rotating ring, and gives a lot more height for the tools etc, and you can buy one ready made for some of the foreign imports in our local machine tool suppliers.

The majority of time you will use the lower part of the column, so the upper part if extended will not get in the way, so it might be a good design to just make the column longer and hope it clears the ceiling....LOL......I had that problem in my garage/workshop with the extended Ajax column and also four 100mm spacers I added under the base corners to keep it off the floor so that I can get a pallet truck under it to move it one day......it'a a pain to have to get the mill, weighing 1-1/2 tons, up off the floor using a long lever and packers.
Ian.

[christofer]

I attempted to measure the backlash in the THK ballscrews and I was not able to find any. I may try again with a more rigid setup and see if I can apply more force. It looks like the THK 20mm screws will be the way to go.

My attempt to remake the spindle is nearly done. I only need to cut the recess for the pulley end ball bearings and I will be done. This time I removed the last 1.5 thou with 320 and 600 grit sand paper from the inside diameter of the AC bearing recess. I can just barely manage to get the bearings in and out now. I have a very slight sliding fit I would say. I will do the same for the ball bearings. I have found that about 0.5 thou is enough clearance for the kind of fit I am after.

I sent a quote to a local steel supplier for most of the large steel parts I will need. I was quoted $850 including tax for 800 pounds of steel. I was told they have a CNC plate cutting machine so I provided drawings of some parts I would like rounded edges on. I intend to order some of the smaller steel pieces from metalsupermarkets. They apparently have a store in Nashville that will be convenient.

It was impossible to find a piece of 12 x 8 inch rectangular tube locally so I have decided to put two 8 x 8 tubes side by side to make a 16 x 8 tube with a solid 1 inch thick wall down the center.

I still like the idea of doing an E/G fill when the machine is built. I may wait and see how it performs first as the fill will add weight and cost. This machine already will weigh around 1200 lbs when done plus a hundred or so for the stand.

[TechGuy5002]

It was impossible to find a piece of 12 x 8 inch rectangular tube locally so I have decided to put two 8 x 8 tubes side by side to make a 16 x 8 tube with a solid 1 inch thick wall down the center.

What about just using four flat bar steel pieces to build a tube. using 1 inch flatbar, you would need two 8 x1 and two 14x1 pieces. The pieces could be bolted and welded together.

For E/G, just fill the tube with E/G after you have completed work with the tube.

[christofer]

Here is my second try at the spindle housing. I polished the inside of the bearing recesses with 600 grit sand paper. I also polished the outside of the housing with 600 grit.

I measured 0.0003 inches of runout by spining the spindle by hand. I was able to push the spindle side to side in the housing about 0.001 inches by hand. This is without the end retainer plate machined. I hope once the end plate is machined and the bearings are clamped in the housing I will not be able to push the spindle around.

Here are pictures.

[mactec54]

christofer

Without the front end cap in place, you should be able to move the spindle, because the bearings have not been preloaded, the front cap needs to press on the outer edges of the bearings to apply the preload

[christofer]

I ordered the material for this mill today. Here is a rendering of what it will look like minus the round spindle housing.

[handlewanker]

Hi, half a ton already...hope you have a good stand to mount it on, half a ton is engine crane work to move it.

I knew a model maker some time back who built model live steam locos as a hobby.

His first build was a 5" gauge 4-6-2 Pacific loco and when it was almost finished the stand it was resting on started to collapse from the accumulated weight....it just got heavier as the build commenced without him realising it.

I would hope the spindle run/out will improve when you add the retainer cap....if there is no improvement, the only other solution is to assume the spindle bore is running out to the OD of the spindle itself, a situation you cannot cure unless you regrind the bore in situ when the bearings are assembled in the housing and preloaded.

I would also examine the stated tolerances for the spindle and bitterly complain to the supplier if the tolerance is not as expected and you can't tweak it.....hope you haven't "modified" the spindle in any way.

Sometimes just disassembling the bearings and re-assembling them "cures" the problem, something you come to terms with when you DIY.

It's looking very good so far.

What was the 8" X 12" tubing for that you had trouble sourcing....the column?

The alternative 16" X 8" (twin tubes) will make a more rigid column, even without the centre 1" rib compared to the single 8" X 12" that you wanted to use, especially if you just weld the center walls all the way down the length using short 1" length welds, and then add the base mounting plate.....capping the top with a 3/8" plate too will help.

You should be able to machine two long flat seats, just inboard from the rounded corners down the length of the tube face for the slide mounting without having to add steel flat bars as in the original design.

This will mean less welding distortion to the main column compared to if you weld a 1" rib piece in the centre and also flats on the face of the column.

You will also have to check that you have enough thickness in the tube wall after you machine the slideway seats to tap into.....if this is an issue, then flats approx 1/2" thick will need to be welded to the tube face and machined flat.
Ian.

[rowbare]

There is an awful lot of room between your X rails and Y rails. That might cause some grief. I would suggest mounting your X rails on the table and the X blocks face down on the same plate that holds your Y blocks. You will need a longer table, never a bad thing, and the rails will add some rigidity to the table as well.

bob

[christofer]

Here is most of the structure. There will be a fair amount of processing to do on the material that was flame cut as the edges are a bit wavy looking.

I have to take the structure to a machine shop anyway to have it all machined flat so I may get them to machine the edges while I am at it.

[handlewanker]

Hi Chris, it might pay you to buy or hire an old mill and do the machining yourself.

That way you can cut and try as you go......bound to be a lot of reworks as you evolve the design.

You're brave in having all that material cut and ready to weld.......the design must be pretty well fixed by now.

How about a mock up assembly of the parts as they will be joined prior to welding.
Ian.

[FannBlade]

Here is most of the structure. There will be a fair amount of processing to do on the material that was flame cut as the edges are a bit wavy looking.

I have to take the structure to a machine shop anyway to have it all machined flat so I may get them to machine the edges while I am at it.

I'm excited for you. This is a great undertaking.
I do hope that is not the welder you are going to use for the main structure....?

I hope to build one from scratch myself one day,I will be watching.

[bozidar22]

Is this build still in progress ?

[handlewanker]

Hmmmm, it would seem another thread grinds to a halt with no further progress anticipated....Oh well.
Ian.

[christofer]

After a long break I am back. I have slowly been working on progress for this machine over the last month or so. As with most projects of mine, I fall into and out of interest in them from time to time. I am however back on this mill now for a while. I am fairly close to having the structure built so why not make some more progress now.

The spindle is as done as its getting for this stage of the project. I reground the inner races of the larger AC bearings and now have some preload on both sets of bearings. The working end of the spindle deflects about 0.0005 inches if I put about 150 lbs on it. I would like to get this lower but perhaps it will take me remaking the spindle yet again once the machine is working. The runout is still about 0.0003 inches as it was before. I packed the bearings with grease which will hopefully not fall out of them over time. I made a seal for the top AC bearing near where the drive pulley will attach. Finally, I found a shop to machine me some clamps to hold the spindle in place on the machine. The spindle will be driven by a V belt from my 2.5 hp treadmill motor that is seen earlier in the thread.

I have been working on machining the various plates I have for this build to be flat and square. It is hard to cut flame cut steel as I have discovered. Carbide inserts work well but tend to dull after a few minutes. I am nearly ready to weld the head riser section of the machine together. After that will be the column and the base.

I have ordered a gallon of epoxy from us composites for use in leveling and flattening sections of the machine. I believe this will be a lot cheaper than having these sections machined to be flat square. For the mounting of my linear rails, I am considering using epoxy granite rather than steel to raise the rails off the base and column. I could cast inserts into the epoxy granite to avoid having to tap lots of holes in the steel structure. All the threaded holes for linear rails in the base are 1/4-20 so the inserts could be 7/8 inch long coupling nuts welded to the steel base then cast over with epoxy granite. The epoxy granite would likely be a mixture of things I can buy at lowes such as general purpose gravel and sand. The orange areas of the picture I have attached show where some material needs to be added, Whether it be EG or steel. EG would be a lot cheaper though and would save me taping 50 or so holes.

Attachment 204102

Before any EG is applied to the structure, the whole thing will be stress relieved. I was quoted $200 by a shop here in town to stress relieve everything and bead/sand blast it clean.

Does EG stick to steel well?

I found that BK15 bearings from ebay work well with my ballscrews. I discarded the included AC bearings that came with the block and transplanted the super precision bearings that came with my THK screws. My screws are THK ground screws of 20mm diameter and 4mm pitch. I believe they are C3 or better precision. I have two idnetical screws I will be using for the Y and Z axes. These screws have about 14 inches of travel. The X screw is still to be determined.

[handlewanker]

Hi, some projects just get to you and you need to have a break.......best of luck in the build.
Ian.

[bozidar22]

As with most projects of mine, I fall into and out of interest in them from time to time.

Been there done that too. Good to see your back.

[christofer]

I have more progress to report on my mill. I have been testing various mixtures of polymer concrete to find what I like best. I went to Lowes and bought play sand, general purpose sand, and gravel. I made two 4 ounce batches of epoxy and from it did one flat pour on a steel plate to check for self leveling capabilities. I seem to have easily hit 0.001 inches of flatness on the 6 inch square pour I did. I did not use a heat gun or blow torch for any of the work but still hardly had any bubbles. This epoxy is very thin and bubbles mostly pop themselves.

Of the three test batch's of polymer concrete I made, I like the general purpose sand the most. This is the dark brown one in the attached pictures. It likely has a packing density around 0.65. The playsand has a packing density of about 0.62 and the gravel alone has a packing density of 0.66. For play sand and general purpose gravel I used about 30% epoxy by volume. That is I put 30% as much epoxy as sand in the mix. For the mixture of gravel + play sand, I used about 17% as much epoxy as sand/rock.

I will likely use general purpose sand for the mounting of the linear rails and play sand + gravel to fill the frame of the machine. Attached are pictures for your viewing pleasure.

[christofer]

More progress made today. The tubes for the base are now bolted together. I took my drill press and put it on the floor to drill the holes in the tubes. I also tested my polymer concrete samples today by hitting them with a hammer. This stuff is very tough. While the playsand mix has fewer voids in it than the general purpose sand, I really like the look and feel of the darker mix. Perhaps I will compromise and use some of each sand.

The play sand was unwashed by me. The general purpose sand was washed because it was super dusty. Both seem very strong. I hope they are hard enough to mount linear rails too.

[christofer]

Yesterday I bolted the tubes together and today I welded them. A granite surface plate was used to make the top surfaces of the tubes line up. This thing is about 300 pounds now in weight.

I hope my welds are strong enough. I used 3/32 inch electrodes of 6011 at about 100 amps.