[Jason Marsha]

After contemplating it for a while I decided to make a start at building a router that could hold at least a full sheet of plywood. this wouild be my third router but the first metal one.

I have access to 2" by 4" rectangular hollow section metal which I will use for the bearing assembly pictured, to run on. I left a space between the bottom bearings in order to support the long axis.

I also have access to lots of skate bearings(608 series) from frequent copier scrapping and the 5/16" threaded rod is cheap and strong enough to tie the whole assembly together, it also fits the bearings with minimal play.
It looks I should be using in the region of 64 bearings which will be no problem.

The solid metal bar that makes up the corners of the runner assembly is 16mm (~5/8") square and was a pain to drill even after marking the holes with a center punch. After having the drill bit wander too many times I went looking for Black & Decker's bullet point drill bits or DeWalt's pilot point bits. These bits have a tip somewhat like a brad point bit for wood but the pilot or bullet point bit will drill metal, wood or plastic.

I will get some hollow section this week to give a visual idea of how the setup will work.

It appears that gear track will be the mode of motion for the long axis which then raises the question of whether the long axis will be driven from both sides, one side or the middle.

My CAD skills are ok but I should make up for that with lots of pics.

Jason

[randyf1965]

WOW! Looks like i is going to be a big machine if those are the linear bearings

Are you going to tie the bottom of that assembly together? Seems like it would splay out on the bottom.

[Rodm1954]

John,
I found it better to place a couple of washers between the double bearing when I trialed it. There is a bit of play between the threaded rod and bearing and one beariing always lifted higher than the other. It is only slight but if you hold the bearings and spin the threaded rod you can feel it. The washers between the bearings spaced the bearings slightly apart and helped. Hold the bearings against a flat surface as you tighten the threaded rod and you should get a better result.

[Jason Marsha]

The problem with tying the bottom together is that there would be no way to support the long axis. The top of the bearing assembly would be fastened to the assembly on the opposite side so there should be no problem.

Jason

[randyf1965]

doh! yep

[Jason Marsha]

Rod
I have also felt that movement, I was thinking however that when I tightened the whole assembly to the running surface all the bearings would at the same level together.

Jason

[joecnc2006]

Rod
I have also felt that movement, I was thinking however that when I tightened the whole assembly to the running surface all the bearings would at the same level together.

Jason

The bearings should pull up tight to the threaded rod and have no play when tightened from both side.

Have you thought about belt drive for both sides for the X Axis?

[Jason Marsha]

Joe
I guess I was avoiding belts but I may have to consider them if they will give me the most bang for the buck. Has anyone used belts with sucess in the forum?

Jason

[spalm]

Benny used belts and really liked them.
http://www.cnczone.com/forums/showthread.php?t=6143

Steve

[Jason Marsha]

Thanks Steve.

Jason

[Jason Marsha]

After giving belts an examination it seems that they may be the best option for me. Belts can be rolled up and easily transported eg suitcase, that would be a bit harder with gear track. I have family due for a visit to the island soon, so I will probably have them bring the belts for me.

I like Benny's design as well as a design from Europe, I will probably rig up a hybrid of the two machines. My only concern is the belt stretching. Is there a special type of belt for this application?


Jason

[spalm]

After thinking about this, belts do seem like the easiest and cheapest way to go. 10 feet rules out screws. Have not priced gear track, but seems expensive and hard to gear down and align. With a 5 foot wide gantry, I would think you need to drive from both sides. Use an axle at both ends, with split belts tied to the gantry. You would only need one motor that way, driving the axle in the middle, under the table.

Seems like everyone goes to SDP/SI for belts and gears.
http://www.sdp-si.com/

Dang, this seems like a fun project, especially if you are getting some of the components for “free”.

Steve

[Jason Marsha]

Thats right Steve, SDP/SI has a very wide selection of gears, belts and pulley parts. They seem a little pricey but quality is what matters.
I will ask Benny what is the pitch of the belt he is using for his machine.

Jason

[randyf1965]

You might want to down the belt drive doc . loads of info

http://www.sdp-si.com/D757/Libdownload.htm

[Jason Marsha]

Thanks Randy,
Downloading as I type. I suspect this information is in one of the catalogs they sent me a while back "Handbook of Timing Belts and Pulleys". Its full of info on what belts and pulleys to use, actually I think its a bit much (information overload) :drowning:
I went over to Benny's thread and saw that he had used T5 , 16mm wide belts.
From reading the SDP/SI catalog the GT2 belts seem to be the best to use, I will have to check the cost first to be sure.
If the cost is right for me I will probably go for the GT2 5mm pitch, 15mm wide belt.
I think I will have fun with this project.

Jason

[Jason Marsha]

Due to length, that belt I want is a special order. I will email them and see what they quote me.

Jason

[Jason Marsha]

The smallest pulley recommended for this 15mm wide belt is a 18 groove pulley. If I drove the shaft with the pulley attached is driven directly with the stepper I would be moving the axis about 1.1* pi inches (27.94 * pi mm) per turn of the motor. At 500 rpm those figures translate into 1727.88 inches (43,888 mm ) per minute which seems awful fast and I suspect I would need a rather strong stepper to move the gantry back and forth even at a slower speed. It looks like lots of gearing down in order

The pulley info has pitch diameter and outside diameter listed I am not sure which to use for step calculations.

Jason

[keyne]

Jason,
movement per rotation is effective diameter * pi. I suspect it is more than 28mm with an 18t pulley. Actually i think you forgot to multiply by pi.
550ipm doesn't sound *that* fast.. how about 1650

What european design did you refer to earlier?
Regards
K

P.S. i will start a build log/planning log for my machine soon, also a belt driven design.

[ShayArnett]

Sweet with you and Joe both working on 4x8+ designs, by the time i finish my jgro, and build joes 2006 you guys should have some nice designs to look at for expanding further.

Keep it comin!!!

[bigz1]

How much do you think belt slipage and stretch will effect accuracy/precision on a design of this size?