Adhesive tape for mounting the racks - does it really work and where do we get it?
 

What have you found to be the best way to attach the rack to the angle iron?

Looked at the PDF and it appears as one bolt either end (I think)

Thanks.

Drawings 1010200A and 1020200A refer. Good double-sided tape along the whole length - the bolts are only for belts & braces. 3M is the only brand name that I know making quality tapes. Use 2mm thick tape. See the VHB range. Make sure that the metal surfaces are properly degreased before applying adhesives or paints.

Gerald...
According to the drawings and posts, the racks are attached to the rails with the two end screws and double sided tape. Is there a reason one should not attach the racks (on the X axis) to the channel iron, rather than the rails?
Thanks...

Hi Bill

I sense some nervousness about the double-sided tape.....http://www.mechmate.com/Forum/clipart/happy.gif

The channels are not an accurate reference surface, probably not straight either. There is a clearance of about 3mm between the rack and the channel. You could be spending a lot of time to fill that gap with shims of varying heights.

Properly applied d/sided tape has become accepted in the metal engineering industry for "structural" use. On the MechMate, even the d/sided tape is an overkill because the stresses on the long racks are very low. The end-screws are enough to hold the racks, the tape is only to stop the racks from sagging under their own weight.

(Those semi-trailer trucks without all the old-fashioned rivets showing, are sometimes held together with d/sided tapes.)

Actually, my thought was that there would be some flex in the rack (pressing the tape together) as the pinion gear travelled back and forth, shortening the racks lifespan and adding wear to the gears... although the tape may be fully compressed after just a few passes... in which case, the problem is a moot point.
Just a thought.
Thanks for the input...

I don't think the compression of the tape is a factor at all. The pinion force is relatively low, the 16mm [1/2"] square rack is fairly stiff and the tape area is big. I did some measurements while experimenting with backlash in a non-springloaded pinion system and didn't detect any tape compression at that time.

Man, that 3M tape is strong. When I build my next Mechmate, I think I'll stick it all together with this stuff rather than welding it.:)

If anyone is looking for a good source for 1/2" wide, 2mm thick, VHB 4955 tape from 3M, try Uline.com

http://www.uline.com/ProductDetail.asp?model=S-10148

Suggested retail price is around $85 or so but Uline allowed me to order only one roll, delivered it to my house in two days and only charged $61 total.

VHB tape is a very familiar to anyone in the sign industry. Almost every local sign supply shop that carries roll vinyl, sintra or plastics should carry it. 61 dollars is a little high. You should find it for around 45-50 dollars for a roll locally.
Another good thing about VHB, it is self activating after 72 hours. Which means if you think its strong on immediate tack, wait three days.
Sean

Just saw a show on tv last night that showed how 3M VHB is being used to "weld" the aluminum skin on transport truck trailers now instead of rivets. They showed some demos and the tape joint was much much stronger than the riveted joint. Amazing stuff!

Paul

Tape has been ordered.. Found 5 rolls of 3.5 meters on ebay for 16.5 Euro including shipping to Denmark...:-D An offer I couldn't resist....:D

The VHB tape is also typically available at automotive paint supply stores. When I realized I'd bought the wrong stuff online (the thin film) I was able to pick up a roll of the 3m foam there at a good price.

Chuck

Copied from a personal thread:

Please drill and tap your 6mm holes for the racking. I left it till last because I was not sure if everything that I did was 100% up to the dimentions in the plans. I thought I will put it together, mount the motors and check that the pionions REACH the rack at the correct position. Trust me and prepare your racks to fit flush on the side of the X and Y rail...they will fit. I had to take the Y-rail off last night to drill and tap. Tonight or sometime this weekend I will have to take the X-Rails off to do the same there....lots of extra work.:(

Kobus, you do not actually need the screws in the end of the racks. I put them in the design for the folk who are nervous about the double-sided tape. :)

"Trust me and prepare your racks to fit flush on the side of the X and Y rail...they will fit." The perfectionists may argue the flush aspect since the drawings show those tapped holes as 7.5mm [0.3"] from the edge, while metric racks are 16mm wide and inch racks are 0.5" wide. Also, the clearance holes drilled through the rack are shown as 8mm[5/16"]. The holes in the rack can happily be increased to get the racks flush if you want - remember, those screws don't actually do anything ;). (ShopBot only use tape, and there have been rare reports of racks falling off. But, their care in selecting the tape and cleaning the surfaces is unknown)

Thanks Gerald, will try the X-Rail just with tape...always eager to try the UNKNOWN....maybe I am lazy as well :p

I have been using a shopbot PR96 since 1999. I have had no problems with the racks coming loose. I would like to remove the racks and re-use them with the Mechmate upgrade. Is it difficult to remove the racks?

Jimbo, I don't know how thick your tape is, but I have had success with using a breadknife to saw through the tape and then a powered wire brush to clean off the residue.

My brother has removed the glued in windshields from cars using a fine wire pushed through from inside to outside then wrapped around some sticks and pulled around the perimeter of the windshield. This process just might work with racks?? Try some small fishing leader (25lb test) it's tough stuff.

JR,
I have used steel guitar strings for this purpose. Might work with the tape as well?

Anybody have a partial roll (9-10yards) of VHB 4955 tape they would be willing to sell?

Thought I would ask before purchasing a new roll.

Wayne

VHB 4955 is not available in Belgium or the Netherlands.
The offered alternative is VHB 4991 (thickness = 2.3 mm)
Tomorrow ,I am going to try the Y-rack without using the extra bolts.
I'm curious about it ?

2.3 mm is okay

A couple of people have built their tables without mechanical stops at the ends of the rails. In these cases the pinion gears will hit the "extra bolts" and cause a bit of damage to the pinion gears. It is better to leave out the bolts/screws at the ends of the rack if you do not have mechanical stops for the gantry/car rolling off the rails.

Today I have already cut the rack loose of the rail with a stanley knife.
I know now that 3M VHB 4991 is strong enough to hold the rack under the rail.

Sources for the 3M VHB tape ??
 

Hi everyone
As for this VHB 4955 Tape, I’m trying very hard ( few hrs on the net ) to find some and NIET, NADA !
Substitute, sure but 4955 series....NADA :confused:
Maybe me, but tried MSC, CarrLane, McMaster and some local one....still ZIPO :o
Again, maybe me having a difficulty searching or is it VERY hard to find ?
May someone give me a link to a valid stocking vendor or a valid replacement !
Merci, Robert ;)

Robert,
Try uline.com.

http://www.uline.com/BL_6051/3M-4955...ylic+Foam+Tape

It looks like they stock it and have a Canadian office.

Carl is right Uline....

Thank you V-much for this ! ;)

After I paid an exhorbitant price for a big roll of the stuff, someone suggested that I should have checked with the local sign making shops to see if they would sell me a few feet of it.

Robert,

I ordered the wrong tape from Uline. Not the only dummy around :o

Sooo, I attached my racks to the underside of the rail with Gorilla Glue. A little bit goes a long way. Have not experienced any problems or issues. Worked great.

Greg,
Really?! What a great idea.
Did you clamp the heck out of it to keep the expansion rate even across the length of the rack? I'm going to have to go out the shop and do a metal to metal sample now!
Sean

Greg...Interesting...
Funny as I have a plan B if I could not easely or no longer able to get the tape, I was thinking to search for some sort of glue, 2k epoxy, but never I would of thought stretching my arm to grab some polyurethane Gorilla glue for metal!!
Yep...true, Gorilla does advertises it can glue metal…dam I like this glue more & more !!

Gerald, would there be some advantages to use 3M tape aside of maybe easier to remove ?
Any advantages to have this little dampening out of the form core ??

Sean, give us some feedback about your test :eek:
Robert ;)