Originally Posted by
southernmema
My Singer 201-2 will usually do it.
I was going to suggest a 201 as well. About six months ago I was modifying a pair of 1970s jeans and my 66 couldn't easily sew four layers. Pulled out the 201 and it powered through it like it was sewing butter!! Your denim is obviously heavier but my 201 is the only domestic I sew denim on and use it for anything denim now with no problems yet.
Of course an industrial would be better still, but 201s are unusually strong machines. Get one and you'll love it forever.