Build Thread- Finally building a JGRO

[jcdammeyer]

Well finally got started on this. Attached is a photo of the Z axis and a couple of patterns for the router carrier. I still have to make the patterns for the rail carriers and then I'll cast the works out of aluminium.

I'm also going to epoxy pot thread inserts into the MDF for the Router clamp bolts.

My biggest issue so far has been tapping the UHMW with my home made 1/2"-10 ACME thread tap. I made the tap from some ACME threaded rod but it's not the best for this. For one thing. It's the same size as the threaded rod. A standard machine tap is usually a bit larger than the bolts that are threaded into the holes.

Either I have to buy a proper ACME tap or think about creating an oversize ACME tap that takes into consideration the stretch and springback of the plastic. Currently it's just too tight.

More pictures as I go along.

John

[Ayjay]

Try putting the UHMW in the freezer overnight. This will shrink it a small amount and if you tap it while it is frozen it will expand when it thaws and your fit should be slightly looser.

[jcdammeyer]

Originally Posted by Ayjay Try putting the UHMW in the freezer overnight. This will shrink it a small amount and if you tap it while it is frozen it will expand when it thaws and your fit should be slightly looser.

Thanks. I found that suggestion elsewhere on CNCZone and tried it with my test part that had a very tight thread. Once it warmed up the fit was just about perfect. I'll try a few more tests before I do the real thing.

Excellent suggestion.

John

[jcdammeyer]

Shaft adjustment block patterns are done. Small disaster on the Gingery Lathe when one of the large block patterns came loose and broke into many pieces. Wasn't held down on the faceplate well enough when I was cutting the inside taper. So I'll pour 3 at a time and do three pours instead of two. That will give me one spare.

Should be able to cast these in a day or so. Then I'll have something I can use to mount the rails for the Z axis now that I have the raw material cut for the X carriage.

Slow progress what with all the other projects on the go but making patterns is theraputic so I don't mind the time.

John

[jcdammeyer]

So here they are. After a break of more than two years from casting anything, the Z Axis adjustment blocks are done.

Next step, mill them with the appropriate holes and stuff and assemble onto the X Axis carrier which still needs to be finished.

There's something so primal about casting metal objects. True I could have probably bought aluminium stock for the price of the primer, paint and sandpaper but that isn't the point of a hobby.

John Dammeyer

[DeadTom]

John,
Looking good, keep up the good work. I am just the opposite from you I have my JGRO machine up and operating and I am just now getting into casting some aluminum. I will try the lost foam method as I should be able to make most of my patterns on the JGRO, the first castings will be new adjustment blocks for the JGRO.
DT

[jcdammeyer]

Thank you. It's slow but I feel like I'm making progress. Momentum will stop as we head off to Greece for a short holiday.

Question though. How are the base end plates fastened to the base and the top panel. The drawings have screw and bolt holes for everything except that. Unless I'm missing something.

John

[DeadTom]

I modified my base plate as I did not want to build all of that smaller mdf detail.
I will attach an older photo and in the photo you will see my sacrificial piece of mdf and that is sitting upon and screwed down to the 4 pieces of angle iron. Rigid enough for what I need, oh and by the way yes those are lead weights as my hold downs they have since been replaced with real hold downs. This picture was taken the day I got everything finally up and running.
DT

[jcdammeyer]

Thanks for that picture. Great to see a slightly different approach to the base. I like your motor mounts too. Very innovative.

John

[DeadTom]

The lead screws (Acme thread) are supported on each end with bearings and pinned so they will not move in or out and then on the motor end of the screw I have a few extra inches hanging out so I can get the Lovejoy couplers hooked up. The couplers are actually inside the mounts, this I thought would maximize the traverse area for the table.
A quick question regarding casting aluminum; How large of a crucible would I need to to say 4-6lbs of aluminum? Or, in your picture above, how many pounds of aluminum did your need to cast the adjustment blocks?
Thanks and post some more pics when you get a chance,
DT

[jcdammeyer]

Hi,

In the past when I built the Gingery lathe I had writen (somewhere) the ratio between pattern weight and what the aluminium weighs. Just a sec....

Pattern weighs 40gm, end result without boring the small plug in the middle is 142gms (.313 lbs). That's a ratio of mdf to aluminium of about 3.5. Add 3/4 lb or so for the sprue and same or a bit more for riser and you will know how much aluminium you need for a pour.

I have a #6 silicon carbide crucible which holds, when full to the brim about 6 lbs of aluminium. In this pour I filled the cruible with scrap and a few ingots (about 2 lbs I guess). Then as it started to melt and there was more room I added enough extra until I was about 2"" from the brim so I figure I had about 4 lbs. I should weigh all the bits. hang on....

1.53Kg for the entire melt (3.4 lbs), 0.288Kg (.64) for the sprue. Time from cold furnace to pour with the furnace open a few times to add material and skim off the crap (some of the raw material was dirty) was 14 minutes. IIRC, my calculations in the past means I used about 1.1 lbs of Propane to do this so at about $1 per lbs total melt cost was about $1.20 or so as the aluminium was free. But, I didn't degass the melt so there is a tad bit of porosity since it was dirty casting material.

Hope that gives you a bit of a guide.

John

[DeadTom]

John,

Thank you for sharing that very useful information. I too will be using a propane fired burner and hearing the melt cost as so little really impresses me and reaffirms my decision in attempting to cast my own parts.
Ok, now that is over with how is the build proceeding?

Thanks,
Tom