How flat should my 2.5" x 1.5" rectangular support tubes be?

[Chuck Keysor]

Hello Shopbot friends:

Per Brady Watson's recommendation, I have purchased two steel rectangular (1.5" x 2.5" wall thickness 3/16") tubes. These will be welded onto my X car to better support the rails and to stiffen up the X car.

Before I try and cut them to exact length and square up the ends, I checked out the flatness of both tubes. One has a crown, of roughly .016", mostly centered. The other has a few smaller waves, of about .008" to .010".

While I would assume that the most ideal situation would be to have both tubes be exactly the same and perfectly flat, I don't have either.

However, I don't know if this is enough to worry about. But since I am trying to improve my machine, I don't want to waste $140 of new steel by welding in something that isn't right.

Should I send these tubes off to a machine shop to have them flattened? Should I do something else?

Thanks, Chuck

[Brady Watson]

Chuck,
If they charged you $140 for 2 crowned pieces of steel, you're getting ripped off. My local steel yard has 2.5x1.5x.1875 wall tubing for $88 - that's for a full 24' length. There should be zero crown or twist in those lengths of steel across only 6 feet. I would expect there to be some across a 24' length, but no way across only 6'. You should be able to lay it on a true surface (table or edge of X rail) and not see any light between them.

In posing the question, I think you already knew the answer...garbage in = garbage out. If you put twisted/crowned structural parts on your machine, anything sitting on top will also be crowned or twisted. Not sure if you can take them back or not. The only other thing would be to try to true out the crown in a press - but again, steel is cheap and I would just get new ones that were straight to begin with...and not buy them unless they passed a straightness test at the yard.

-B

[Chuck Keysor]

Thanks Brady. I guess I have to search for another source.

I called a few local steel supply houses, and found either no stock in this material, or they wouldn't sell retail. I finally called the friend who will be doing the welding, and that is how I found the source that I used.

My welder isn't a machinist, so perhaps he hasn't had to worry about accuracy. And myself being totally ignorant of steel specs, didn't know what to specify for flatness/straightness. I guess I still don't know. Do I have to ask for something such as machine grade flatness (whatever that may be)? I am at a bit of a loss as to how to avoid repeating my mistakes. :confused:

Making it more frustrating, none of the 4 ends were cut square. (Though I did have each piece cut an extra inch long,,,,) And t
hey also originally wanted me to purchase an entire 20 foot long piece. I felt like I had won a concession by only paying for what I wanted to buy. :(

Thanks, Chuck

[steve_g]

“they wouldn't sell retail”
“wanted me to purchase an entire 20-foot-long piece”

Chuck…

In my experience, I’ve found that the metal building suppliers are most willing to sell in small quantities, but still expect you to buy full sticks of metal. Usually we can buy a full stick cheaper than someone else will sell a cut stick of any length!

I keep two business names, SG mfg. and Treasures from Trees. I do this because “wholesale only” suppliers are more willing to sell to the mfg. name while “craft” and “custom” purchasers hesitate at the mfg. name. In either case, it’s necessary to have the appropriate sales tax ID numbers…

SG

[Brady Watson]

You won't hurt anything going 1.5 x 3.0 x .1875/.25 wall. It'll just hang down another 1/2"...big deal.

OnlineMetals is convenient if you can't do B2B. They have 2x3x1875 precuts (https://www.onlinemetals.com/merchant.cfm?pid=12876&step=4&showunits=inches&id=241&top_cat=849)...I would call and tell them you need them to be straight...but any major city should have a steel supplier (more than one) - where you can order up what you want. You don't need to have an actual company to do B2B. Just make up a name - tell them you are paying cash & it's all good. Some will even do CC. You are not tax exempt - that's it.

If you have to take the drop from the 24-footer after they cut it (specify SAW cut & not torch cut), then so be it - it's good fodder for your practice welds... It's steel...there's always a use for it in the shop. It has to be steel because you really want to weld up the entire gantry to stiffen it up - Plus, you want the stiffness against deflection that only steel brings to the table.

Welders have gotten REALLY cheap in recent days...With a budget 14" chop saw, 4" grinder and MIG welder. - You could do all mods yourself, PLUS build a 2nd machine or further mod your existing, if you so desired...Sometimes you just have to take matters into your own hands because life is too short for other people's sad stories when it comes to getting what you want...or make your mods and sell off the welding stuff when you are done.

Failure is not an option. Be unstoppable. Don't take no for an answer. What one man can do, another can do. You need to remind yourself of that from time to time & just Git Я Done!

$300 @ Horrible Freight:
Flux core MIG $189 (https://www.harborfreight.com/170-amp-dc-240-volt-migflux-cored-welder-61888.html)
14" Chop Saw $97 (https://www.harborfreight.com/14-in-3-12-hp-heavy-duty-cut-off-saw-62459.html)
4-1/2" Grinder $15 (https://www.harborfreight.com/4-12-in-43-amp-angle-grinder-69645.html)

-B

[Chuck Keysor]

Thanks Steve for your insights on how to deal with different business entities. I never would have thought of it, but what you said makes sense,,,,,,, thanks...…

Brady, thanks again. Now, in the spirit of trying to move on and get things going, it occurred to me that the side supports that hold up my 14 foot X rails, are both crooked as can be, and that the X rails are carefully set up on shims and spacers to get the X rails as straight as can be, and parallel to each other. So why shouldn't I be able to do the same thing with my new rectangular steel tubing? I'll just have the tubing welded maybe 1/8" below the Y rails, and then use carefully selected shims to make the Y rails flat and straight. Any problems with doing this, even though it isn't elegant???? Thanks, Chuck http://www.talkshopbot.com/forum/attachment.php?attachmentid=31968&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=31969&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=31970&stc=1

[Brady Watson]

Chuck,
You're going to want to weld a 1" long bead on the side of each Y rail to the top of the 3x3 after you've got everything 100% perfect. Make spreader blocks to keep those rails 22" apart, tack everything and check it six ways from Sunday. If you want more Z clearance, add a 2x3 (raising it up 2") on top of the 3x3 and weld it up. If not, keep it as it is.

I wouldn't personally use them being such short length and having a crown in them. They're only $3.70 a ft for me, so they'd get chucked on the 'farm use' pile. If you have to shim them - go for it. At the very least cut the shims back so it doesn't look like a beaver in a headlock...;) I'd also want to cut them myself because who knows how square their saw was...almost certainly not good enough for a CNC...but nothing a MIG can't fix in proper hands.

-B

[Chuck Keysor]

Hello Brady! Thanks again for your information....

Relating to increasing my Z capacity..... I DO want a greater capacity than I have. (I once had a chance to process a bunch of 5 1/2" thick foam and was disappointed to find out that it was too thick for my machine.)

Not wanting to go back to the place that sold me the previous rectangular stock, I called around again, and got stuck. So I found a local scrap yard that would let me pick through their piles. I found 2 inch square and 1 1/2inch square tubing, with 3/16th inch walls. I bought two 30" long pieces of each size. (Total cost for all 4 pieces was $15..... I clearly have push-over painted on my face...)

Can I stack these tubes up, to raise my Y rails by 3 1/2 inches without messing something up? (If I hadn't taken my machine apart, I would have tried to figure this out, but I still would have asked to make sure...….). If not, I'll just use the 2" tubing. (I could sell the 1 1/2" tubing back for 6 cents per pound :(.)

Thanks again,,,,,,,,,, Chuck!

[Brady Watson]

Chuck,
Question: What are you expecting to gain, aside from increased Z height by doing this work?

I try to just say things 'how it is' - and some people can't take that...while others appreciate the honesty. Hopefully you fall into the latter. Before you do anything to that gantry, consider how it will look adding the components that you mention. Personally, I think it would look like a hack job and there's no way I'd want my machine (or yours) to look like that. Not that the PRT wins any beauty contests...but, you gotta use the right stuff. I don't want to see your machine on There I fixed it (https://www.popularmechanics.com/home/how-to-plans/how-to/g519/10-hilariously-bad-home-diy-projects/)

My compelling motivation for welding up my original PRT gantry was two-fold. First, I was tired of the gantry going out of square and the arduous process of getting it square and parallel again. It is a nightmare (but not so bad for me now having cut my teeth on them) - the second reason was stiffness and resistance to deflection under the weight of a heavy Y car with twin Zs.

If you aren't having any issues with Z deflection/sag, then you can probably forgo putting steel under the Y rails and just run what you have. I would take a good look and make sure it is secured properly. I would however, run a weld bead where the Y rails attach to the 3x3s. This will keep the gantry from turning into a parallelogram. I'd run a total of 4 one-inch beads per corner. Two beads on the flat part of the angle (along the 3" face - space in the middle) and the same on the outside of the rail - then repeat on each corner. This is of course after tack welding all points to keep the heat from racking your otherwise true gantry.

In terms of raising the gantry, you don't want to go more than 2" high. You will run out of T-rail unless you have a 12" Z assembly. $25 a piece for 2x3x1875" here (https://www.onlinemetals.com/merchant.cfm?pid=12876&step=4&showunits=inches&id=241&top_cat=849) As it is, the Z barely hits the spoilboard with a small, short bit. Measure carefully.

Use the right stuff...don't settle for less than the right stuff - unless you like sad stories and disappointment. I don't, which has made me be more patient & determined.

-B

[Chuck Keysor]

Brady, my primary objective was to improve my gantry's mechanical stability. It always just bugged me that I had to re-square the gantry every time I turned on my machine.

Maybe a year ago, someone suggested that I use red Lock-tite on all the X-car bolts, and torque them to some specified amount (might have been 80 ft-lbs). But even with that it still kept going out of square. (I sure didn't like that Lock-tite when I started to disassemble the X-car the other day. I had to use a wire wheel on each of those bolts to clean them up and get rid of all that gunk.)

My secondary reason was to eliminate the little bit of sag that I got with my big spindle in the middle of the gantry. It contributed some to my problems with V-carvings.

I had not planned to increase the Z-height until you mentioned it. And now, after looking at it, I have decided not to mess with that.

Before measuring how long the 2.5" x 1.5" steel support tubes need to be, I had to square up the gantry after removing the aluminum supports. I had the two rails 22" apart at each end of the X-car, but I couldn't get the framing square to square up from the angle iron to the aluminum plates clamped to each end of the gantry. Then I discovered that both of the angle irons were bowed in, by about 1/8" on each one. So I wedged in a spacer, to force the middle spacing to also be 22". And, luckily, the bow was evenly divided between the two angle irons, and each angle iron then read flat along the side. And then the framing square squared from each angle iron to the aluminum plates. After getting it close that way, I fine tuned the squaring with two diagonal tape measures. Then I clamped the gantry into place. I'll double check it in the morning, then measure the spaces into which the two rectangular support tubes will go.

Chuck

http://www.talkshopbot.com/forum/attachment.php?attachmentid=31974&stc=1

[tlempicke]

[QUOTE=Chuck Keysor;202125]
Brady, my primary objective was to improve my gantry's mechanical stability. It always just bugged me that I had to re-square the gantry every time I turned on my machine.

You can buy 4130 steel tubing, angles, flats, etc. by the foot. It is used in aircraft construction because of it's strength to weight ratio. It is also "stiff". Once upon a time I tried to put a curve in a piece of 3/4 tubing with a conduit bender and found out that my 200 plus pounds were not enough to do the job.

As you receive it it will be "Normalized" and is quite workable. After welding the area around the welds will be so hard that you almost can not cut it with anything you have in the run of the mill shop. You can anneal it with a propane torch and the information on how to is all over the web.

This stuff welds like a dream. I would suggest, though, that you steer clear of the buzz boxes that HF sells. If you get a decent weld it is almost an accident. Pay a pro to get a decent TIG job and your project will be good for 50 or 60 years of service, just like an aircraft fuselage is.


Take a look here http://aircraftproducts.wicksaircraft.com/category/aircraft-metal-tubes-channels-angles

(http://aircraftproducts.wicksaircraft.com/category/aircraft-metal-tubes-channels-angles)

[Brady Watson]

Mild steel is fine. It's cheap, easy to work, easy to weld and the profiles mentioned should be straight in the lengths for this project. Just shim up the ones you have. Make sure you crown them both in the same direction...(up). You already overpaid for them, might as well just use them.

Before you weld it all up, put the 1.5x2.5 pieces in place and mark out your bolt holes for the rails. If you got 3/16" wall, there should be enough meat there to tap it 5/16-18. Be sure to put witness marks on each rail support piece, including marking the TOP and which end & side the support goes. Then drill/tap off the machine using whatever you have. Be sure to use a punch to mark the centers and if you can, start each hole with a center drill (https://www.amazon.com/gp/product/B00GP9SDLS/ref=s9_acsd_topr_hd_bw_bN0oHT_c_x_w?pf_rd_m=ATVPDK IKX0DER&pf_rd_s=merchandised-search-3&pf_rd_r=A86KTVQQPCWEXHC7DFX5&pf_rd_t=101&pf_rd_p=29b839ad-539b-5131-8880-d0fb070bac70&pf_rd_i=340049011)to keep your larger bit from walking. The cup created by the center drill captivates the big drill and prevents it from walking. You really don't want to 'waller out' holes that are off after the fact. CHECK the threads on your rail bolts to make sure they ARE in fact 5/16-18 (just use a nut) because your setup is an oddball.

Yes, ALL of those angle iron rails splay out when unbolted - so don't worry. Just get them true again when you assemble.

Spreader blocks - 2x6 etc work great for setting the spread on both the 1.5x2.5 and rails. Cut 3pcs for each spread to help. (3pcs for between rails & 3pcs for between 1.5x2.5 tubes. Pipe clamps are also helpful.

You don't need 4130 chromoly @ $45+/foot. I've been welding for 20+ years and have friends who bought the HF MIG for light automotive resto welding. The new ones have come a long way. It works just as well as any other fluxcore MIG. No bottle to put a deposit on, plus bottle rental every month like my shop. You don't need to have these parts TIG welded - just lay some weld beads down to lock it in square and be done with it. You're not welding up an aircraft frame...it's just a ShopBot.

By the way, welding is best done ON THE MACHINE so you can verify that it is square and everything runs true. As soon as you take the gantry out of the shop, you have no way of telling if it is racked or 'out'. I would suggest having a weldor come over and do the work or just do it yourself. What one man can do, another can do, remember?

In doing these mods to the machine, you really have to get over the 'preciousness' of the blue colored steel. It isn't special. It's just steel. Cut, drill, weld on it at will because it's just a pile of scrap if it doesn't do what you want as a CNC. Make it YOURS...then get some touch up paint and make it look all pretty again. ShopBot Blue = RAL 5022

Good luck - hopefully you get in there and just knock it out so you can get back to the business of cutting again...If you lived closer, it would be done already!

-B

[Chuck Keysor]

Hello Tom and Brady!

Thanks Tom for the information on the aircraft steel. That was all new info to me since I don't have metal working experience.

Thanks Brady for the added direction. The welder will be welding my X-car as it sits on my machine, as getting welded up and then finding something is off is the scariest part of this project. The tubing I bought is 3/16" thick, though I have to check my threads and my tap set.

As to the blue paint, I am afraid I messed it up with all the filing I did to get rid of the cold-formed edge burs. (Had I just needed to file a few feet, I could have kept it nice, but I had to file every rail, on both sides, and got sloppier the more I filed. :()

Thanks again, Chuck

[Chuck Keysor]

As a delayed follow-up: Here are some shots prior to welding the rectangular steel tubing into my X-car.

I didn't have a chop saw, and wasn't anxious to buy one. I simply plowed out a tight fitting groove in a 4x4 piece of Douglas Fir that would support each end of the steel tube, and at one end, I cut hacksaw blade guide kerfs, and had a block of steel on top of the tube to help guide my initial cut to make sure I started off perpendicular to the tube before the guide kerfs took control.

I carefully dry fitted the two steel tubes. I went and squared up the X-car before the welding, but I forgot to scrape off the paint from the 3x3 steel tubing first. So I had to resquare the X-car again after scraping the paint and re-installing the steel tubing.

Being used to working in wood, I planned to carefully (of course) the ends of each tube, to get a perfect/tight fit. And I no doubt wasted a lot of time doing this, as steel is not as easy to work as wood! My welder told me later, he would have been ok with a gap of up to 1/8" of an inch. Oh well, next time.

I did NOT drill/tap any of the holes in the steel tubing before the welding. I was convinced that it would be safest to do all the marking and layout of the holes to support the Y rails after the welding is complete. And because the Y rails sit up, maybe 1/4" above the tubing, I will have to make supports (stacks of washers seems too easy) from some scrap steel tubing I bought, and I'll precisely fit those to make the Y rails exactly flat.

Thanks, Chuck
http://www.talkshopbot.com/forum/attachment.php?attachmentid=32065&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32066&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32067&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32068&stc=1

[Chuck Keysor]

Here are the pictures of the welding the steel tubing onto my X-car, just to show some great sparks, then some follow-up shots. I went to my local big box hardware store expecting they would color match Rustoleum for me, but they only sold it as stock colors, so I didn't get a good match....

By bearing down on the middle of the steel tubes, it is clear that this is much stronger than the aluminum supports that came with my machine. However, because the steel tubes are so long, even after welding, I found it easy to deform the gantry to be out of square, though I only did so gently, and it sprung right back to square when I released the pressure. And before replacing the aluminum, if I pulled the X-car out of square, it didn't spring back to square. I suppose having the Y-car sitting on the X-car will firm it up.

http://www.talkshopbot.com/forum/attachment.php?attachmentid=32069&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32070&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=32071&stc=1

I'll post pictures after I do all the drilling, tapping and mounting of the Y-rails. I hope to do that before the end of September...……. :confused: But I have to put the gutters on my house, which I bought last year, and only got part way done. Chuck

[Brady Watson]

Sherwin Williams (not to be confused with Sherman Williams (https://www.imdb.com/name/nm0931690/)) can color match it to RAL 5022 if you want it to match exactly....However, what you have there is close enough and I doubt anyone will even notice, besides you. Last I checked, they can do a custom color in a rattle can for around $35 ea. Not cheap, but it's all you'd need and it will match perfectly. Take a motor mount or something to match up on their machine just in case.

It should be pretty stiff & unrackable now! Drilling and taping the holes shouldn't take more than 2hrs...