[79TigerPilot]

I am just starting a project to build a mobile base for my J-head Bridgeport and though I would start a build thread. Best I can figure the BP ways in just north of 2200 lbs is quite difficult to move around even on roller rods. The BP had been sitting in the middle of the shop getting converted to CNC but now needs to be moved to a new location. Not only will the mobile base allow me to move the mill around it will raised the base up about 3-1/2" to accommodate the new longer ball screw I recently added on the knee drive.

Initially I was going to put a wheel on each side of the base at the center of balance but I found the balance range was only about an 2 inches so I changed the design to use three wheels. It will have a castering wheel in the center rear and two non-castering wheels up towards the front of the base on either side. All the wheels will extend and retract by hydraulics using a base mounted hand pump. When off the wheels it will sit down on 4 adjustable 2.5" dia. leveling pads. This should be a fun project and a good learning experience. To make it even more of a challenge I will be making my own hydraulic cylinders and hand pump. Though I haven’t finished up the base’s CAD drawings I have started milling out the hand pump.

The pump body starts out as a 3.5 x 3.5 x1 inch block of CR steel. Been very interesting drilling deep passage holes. Had one #24 drill that was about 3” deep. The chuck loosened up part way through and the bit got stuck. Vise grips to the rescue –no harm done. Then, trying to drill the ½” hole 2.5” deep for the pump piston cavity I broke off the a ¼” pilot hole bit down 1.75” . Had to use an end mill to cut the drill out then over cut the hole for a brass sleeve, better that way anyhow. So far all the drilling has been by CNC. Problem is you get no feel like a drill press.

[79TigerPilot]

The hand pump is progressing. I have all the passages drilled, fulcrum machined and the brass piston sleve ready to go. I still need to turn the piston pump rod, and make the two valve poppets. Only had a few minor machining glitches since the broken drill in the pump cavity. I did end up drilling one of the passage holes in the wrong spot. I re-drilled the hole and will just plug off the wrong one.
I had accidently measured the wrong spots on the master cad mode.

Craig

[79TigerPilot]

I finished up the hand pump today. The initial tests did not go well, I couldn't suck up any jack oil into the pump. This turned out to be a combination of things. The oil was way too thick, the poppet spring force was too strong and the intake flow path was too small a diameter. I switched from jack oil to hydraulic fluid, used a longer lighter spring, increased the input tubing diameter and profiled the poppet to provide more clearance to the cavity wall for better flow around the poppet. It pumps very well now and will easly make 2500 psi though only 800 psi will be needed for the base.

YouTube video of the pump in action:
HydraulicHandPump.wmv - YouTube

Now on to the wheel acturator cylinders.

[yantra3d]

Congratulations on your success so far... looks like it's going to be a nice design. Thanks a lot for sharing!

[79TigerPilot]

After taking some time off in December I am back working on the mobile base. Today I cut the first wheel mounting plate, three more to go. These plates will hold the forward left and right 5" diameter wheels that get hydraulically rotated down into position when the mill is raised off the leveling pads. The material is 1/4" plate which may be overkill but I needed some thickness for the 1/2" dia flat head cap screw used for the wheel axle. The plate on the other side of the wheel is threaded for the axle bolt. The wheel came with a 3/4" hardened sleeve that accepts the 1/2" axle bolt.

The countersunk hole is almost 1" in diameter on the surface of the plate and I didn't want to spend $50+ for a 1" dia MA Ford for just two holes. So I fabricated my own from some 1" water hardening drill rod. Cut a point at 82 deg on the lathe then cut a flute on the mill followed by hardening with a propane torch. It was a little too much to cut that big countersink hole and the mill bogged down. So I ended up step wise milling an 82 deg slope on the hole with an end mill, then just cleaning it up with my shop built countersink. Worked great at 120 rpm and .1 IPM feed.
Craig

[79TigerPilot]

Today I finished up the wheel assemblies. TIG welded on the top covers and cleaned off the mill scale so they are ready for painting. Now its on to the hydraulic cylinders.

Craig

[79TigerPilot]

I haven't posted an update in a while but I have been making progress. The side wheel assemblies are almost complete. The only thing remaining is to weld the cylinders to the bases.

I spent the last week or so learning how to thread mill. The push rod end of the cylinders have internal threads (1-1/4" -12 ) to accept and end cap/bearing for the push rods. I while back I watched one of Hoss's YouTube videos on thread milling and fugued I would give it a try. Thanks Hoss. I used a DIY milling tool fabricated from a 9/16-12 hand tap. All the teeth except three on one flute were ground off. The tool worked very well and cut nice looking threads but I am sure a real thread milling cutter would work better but this one was free. Only had one D'oh! moment -- the first threading cuts were all conventional milling but on the last part I though I would try climb milling to see how that worked out. So I changed the program from a G2 to a G3 and I got a really nice looking LEFT handed thread. D'oh! D'oh! D'oh!. I just gots to learn to think things through before pushing cycle start.

The first photo is all the parts then assembled with cylinder retracted and extended.

Next its on to the real wheel and its cylinder and finally the frame.

Craig

[79TigerPilot]

Been making progress on the mobile base. The side wheel assemblies are ready to mount after painting and I have started cutting parts for the center rear castering wheel. I should have all the parts for the hydraulics finished up in a couple of days then I can start cutting bar stock for the base frame.

Craig

[79TigerPilot]

Today I did a little TIG welding and sealed off the end of the hydraulic cylinder for the rear wheel assembly. Also welded a flange to the other end. I need to do a lot more practice on the TIG! The welds will hold but they don't look like a stack if dimes by a long shot.

All the pieces for the rear wheel assembly are completed an it has been assembled. Didn't get a chance to test it at hydraulic pressures yet but it works nice on shop air. The total stroke is 2.25" like the side wheels.

Now its on to welding up the base frame.


Craig

[79TigerPilot]

Over the past few weeks I have been working on the main base weldment. I finished up the the final grinding this morning then loaded her in the pickup for a trip to BR&F Spray to get media blasted and powder coated.

This is no wimpy sheet metal base, rails and cross members are 3" x 3/8" HR, top plates are 1/4" HR plate, weighs in at 120 lib without the wheels and hydraulics. It was mostly stick welded (NOTE: got to get a MIG) except for closing the bottom of the hydraulic reservoir where I used the TIG torch.
Welds may not be x-ray quality but they will hold my BP just fine.

My mill is white but decided to make the base black, think it will be easier to match the black with rattle can paint if things get dinged up.

Craig

[Thiel-Metal-Fab]

wow !! thats some excellent work and well thought out . im impressed

[polaraligned]

Wow. Nice!!!

[mactec54]

79TigerPilot

Are you using only 3 wheels for your dolly

[79TigerPilot]

You are correct two on the the sides of the dolly up just behind the leveler pads and one center castering wheel in the rear. The weight distribution should be on the order of 800-900# on each side wheel and 400# on the rear wheel. Will know how it works out in a a week or so, keeping my fingers crossed.

Thanks for the nice comments.


Craig

[mactec54]

79TigerPilot

With that much weight, I don't think it's a safe idea to move the mill with just 3 wheels

In a straight line pushing from the back, it would be ok, untill you try & turn it, then you will have a problem, I have made many machine dollys, but always have used 4 wheels

You need to also rate each wheel with a minimum of 1000lbs each & the diameter of the wheel as large as you can use or get, small diameter wheels make it hard to move a heavy load, unless you use wheels like what is on a pallet jack

The attached photos are of one that I used for Bridgeport machines, But modifided it to do larger machines, this one I use up to 3500lbs I have 3 different dollys like this for moving machines

It is made up of 4 parts 2 end frames with jacks & 2 tie bars that bolt everthing together, once the end frames are under the machine the tie bars join them together, Jack it up them move your machine to were you want, Takes about 5min to set up & take apart

[LUCKY13]

I was wandering about the three wheel setup myself, also maybe even a problem with each wheel not raising at the same rate.



But you have to admit, his hydro system is pretty cool. If it works out ( even if he has to add a nother wheel) it will be great. The workmanship is very good.


Very nice work on the wheel assy, hope it works out and be carefull when testing. BTW I also was thinking some kinda locking system after the wheels reach full travel. You may have that figured in and I didnt read about but if not it might be something to think about. After all even a little tilt from one corner could lead to a crash in the wrong possition when moving.


Jess

[keebler303]

Maybe I missed it but how are you providing even flow to the cyclinders so theat they raise together? If the y are just connected to the same line, you will be able to push the mill and the fluid will run out of one and into the other = tippy!. Might want to make sure that is addressed.

Matt

[79TigerPilot]

Uneven filling of the cylinders will not really be a problem.

All the cylinders have the same throw and volume in addition the throw is mechanically limited by the wheel assembly to 2.25". Normally the weight imbalance between the cylinders will result in one cylinder filling faster that the other two. This is likely to cause an out of plumb condition during the filling process.

Center of gravity measurements on the mill suggests the weight on the rear wheel to be about 400# and about 800# on each side wheel. So I would expect the rear wheel to reach it mechanical stop before the side wheels begin to move. Assuming the front leveling pads are set at 15% of travel (.34") and the rear wheel is fully extended at 2.25" the mill will tilt forward 2.71 degrees.

After the rear cylinder fully extends the side cylinders will begin to fill and lift. The side to side weight difference should be fairly minimal and the cylinders should fill at the same rate. But even if one side fills completely before the other the side to side tilt would be no greater than 3.75 degrees.

Once all three cylinders are filled, a hydraulic lock condition exists in all cylinders, the mill will be plumb and independent of the weight redistribution.
None of the cylinders could retract because there is no place for the hydraulic fluid to go. This would not be the case if one attempted to use air pressure instead of hydraulic pressure.

The side wheels are 5" dia cast iron and rated at 1200 # each the rear wheel is extra heavy duty but plastic will just have to see how it hold up. The saving grace is the mill is normally only being lifted about 1.25" off the leveling pads. If something fails it can't go far and there is little danger of overturn.

My initial design only had two wheels mounted on the sides at the fore-aft CG once up on the wheels you would move it like a two wheel dolly. Decided not to use this because the CG range was so narrow even with a 12" table adjustment, I couldn't be sure I could hit the CG on the first attempt.

Craig

[79TigerPilot]

Yesterday I completed the last items on the mobile base and slid it under the Bridgeport for a test drive. It fit perfect, the mounting holes were all aligned. As expected the rear wheel fully extends first followed by the left wheel and finally the right wheel. At no time does the mill tip more than 3 degrees and is in no danger of tipping over. It takes about 29 light strokes of the hand pump to fully extend the wheels. Rolling force is fairly significant due to the wheel’s tire tread material but once moving it’s not bad and the single rear castering wheel makes it easy to position. The wide spaced leveling pads make the mill very stable when off the wheels.

I now know why tractors are always wet with hydraulic fluid. I swear that stuff will find its way between the atoms in the metal. When I filled the hydraulic reservoir I found 4 leaks, which I had not discovered when I did the initial pressure tests prior to powder coating. I was able to drain the reservoir and solder plug the leaks with minimal impact to the powder coating. Had leaks at 3 bulkhead fitting which I traced down to the “B” nut contacting the bulk head stop nut before it had compressed the flair on the tube.

This was a fun project and a great learning experience in a lot of different disciplines. Now it’s time to clean the shop and decide on the next project, like building the e-cabinet for the mill.

Oh, and I really like the powder coating. So much nice than getting out the spray equipment.

I posted a Youtube video: MobileBase.wmv - YouTube

Craig

[mactec54]

79TigerPilot

Thats great another project out the way,I new it would be quite hard to get it moving as you found out, but once they are rolling it's not so bad

Power coating is great, but sometimes you still have to use the spray